Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Fair Value Measurements by Level for Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)

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Fair Value Measurements - Fair Value Measurements by Level for Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)
$ in Millions
Sep. 30, 2021
Dec. 31, 2020
Assets    
Cash and cash equivalents $ 13,423 $ 10,800
Investments:    
Equity securities 317 318
Other current assets:    
Total assets at fair value 28,893 25,287
U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Assets measured at fair value 656 911
Corporate securities    
Investments:    
Assets measured at fair value 7,827 6,814
Municipal securities    
Investments:    
Assets measured at fair value 3,470 3,097
Short-term time deposits    
Investments:    
Assets measured at fair value 78 53
Asset-backed securities    
Investments:    
Assets measured at fair value 1,148 1,164
Residential mortgage-backed securities    
Investments:    
Assets measured at fair value 911 1,095
Commercial mortgage-backed securities    
Investments:    
Assets measured at fair value 830 773
Investments available-for-sale    
Investments:    
Assets measured at fair value 14,338 13,427
Investments available-for-sale | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Assets measured at fair value 216 165
Investments available-for-sale | Corporate securities    
Investments:    
Assets measured at fair value 7,796 6,789
Investments available-for-sale | Municipal securities    
Investments:    
Assets measured at fair value 3,042 3,070
Investments available-for-sale | Short-term time deposits    
Investments:    
Assets measured at fair value 78 53
Investments available-for-sale | Asset-backed securities    
Investments:    
Assets measured at fair value 1,148 1,164
Investments available-for-sale | Residential mortgage-backed securities    
Investments:    
Assets measured at fair value 911 1,095
Investments available-for-sale | Commercial mortgage-backed securities    
Investments:    
Assets measured at fair value 830 773
Restricted deposits    
Investments:    
Assets measured at fair value 1,114 1,060
Restricted deposits | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Assets measured at fair value 440 746
Restricted deposits | Corporate securities    
Investments:    
Assets measured at fair value 31 25
Restricted deposits | Municipal securities    
Investments:    
Assets measured at fair value 428 27
Restricted deposits | Cash and cash equivalents    
Investments:    
Assets measured at fair value 211 157
Restricted deposits | Certificates of deposit    
Investments:    
Assets measured at fair value 4 105
Other current assets | Foreign currency swap agreement    
Other current assets:    
Foreign currency swap agreement 18  
Level I    
Assets    
Cash and cash equivalents 13,423 10,800
Investments:    
Equity securities 315 316
Other current assets:    
Total assets at fair value 14,605 12,184
Level I | Investments available-for-sale    
Investments:    
Assets measured at fair value 531 481
Level I | Investments available-for-sale | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Assets measured at fair value 216 165
Level I | Investments available-for-sale | Corporate securities    
Investments:    
Assets measured at fair value 0 0
Level I | Investments available-for-sale | Municipal securities    
Investments:    
Assets measured at fair value 0 0
Level I | Investments available-for-sale | Short-term time deposits    
Investments:    
Assets measured at fair value 0 0
Level I | Investments available-for-sale | Asset-backed securities    
Investments:    
Assets measured at fair value 0 0
Level I | Investments available-for-sale | Residential mortgage-backed securities    
Investments:    
Assets measured at fair value 0 0
Level I | Investments available-for-sale | Commercial mortgage-backed securities    
Investments:    
Assets measured at fair value 0 0
Level I | Restricted deposits    
Investments:    
Assets measured at fair value 651 903
Level I | Restricted deposits | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Assets measured at fair value 440 746
Level I | Restricted deposits | Corporate securities    
Investments:    
Assets measured at fair value 0 0
Level I | Restricted deposits | Municipal securities    
Investments:    
Assets measured at fair value 0 0
Level I | Restricted deposits | Cash and cash equivalents    
Investments:    
Assets measured at fair value 211 157
Level I | Restricted deposits | Certificates of deposit    
Investments:    
Assets measured at fair value 0 0
Level I | Other current assets | Foreign currency swap agreement    
Other current assets:    
Foreign currency swap agreement 0  
Level II    
Assets    
Cash and cash equivalents 0 0
Investments:    
Equity securities 2 2
Other current assets:    
Total assets at fair value 14,288 13,103
Level II | Investments available-for-sale    
Investments:    
Assets measured at fair value 13,807 12,946
Level II | Investments available-for-sale | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Assets measured at fair value 0 0
Level II | Investments available-for-sale | Corporate securities    
Investments:    
Assets measured at fair value 7,796 6,789
Level II | Investments available-for-sale | Municipal securities    
Investments:    
Assets measured at fair value 3,042 3,070
Level II | Investments available-for-sale | Short-term time deposits    
Investments:    
Assets measured at fair value 78 53
Level II | Investments available-for-sale | Asset-backed securities    
Investments:    
Assets measured at fair value 1,148 1,164
Level II | Investments available-for-sale | Residential mortgage-backed securities    
Investments:    
Assets measured at fair value 911 1,095
Level II | Investments available-for-sale | Commercial mortgage-backed securities    
Investments:    
Assets measured at fair value 830 773
Level II | Restricted deposits    
Investments:    
Assets measured at fair value 463 157
Level II | Restricted deposits | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Assets measured at fair value 0 0
Level II | Restricted deposits | Corporate securities    
Investments:    
Assets measured at fair value 31 25
Level II | Restricted deposits | Municipal securities    
Investments:    
Assets measured at fair value 428 27
Level II | Restricted deposits | Cash and cash equivalents    
Investments:    
Assets measured at fair value 0 0
Level II | Restricted deposits | Certificates of deposit    
Investments:    
Assets measured at fair value 4 105
Level II | Other current assets | Foreign currency swap agreement    
Other current assets:    
Foreign currency swap agreement 18  
Level III    
Assets    
Cash and cash equivalents 0 0
Investments:    
Equity securities 0 0
Other current assets:    
Total assets at fair value 0 0
Level III | Investments available-for-sale    
Investments:    
Assets measured at fair value 0 0
Level III | Investments available-for-sale | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Assets measured at fair value 0 0
Level III | Investments available-for-sale | Corporate securities    
Investments:    
Assets measured at fair value 0 0
Level III | Investments available-for-sale | Municipal securities    
Investments:    
Assets measured at fair value 0 0
Level III | Investments available-for-sale | Short-term time deposits    
Investments:    
Assets measured at fair value 0 0
Level III | Investments available-for-sale | Asset-backed securities    
Investments:    
Assets measured at fair value 0 0
Level III | Investments available-for-sale | Residential mortgage-backed securities    
Investments:    
Assets measured at fair value 0 0
Level III | Investments available-for-sale | Commercial mortgage-backed securities    
Investments:    
Assets measured at fair value 0 0
Level III | Restricted deposits    
Investments:    
Assets measured at fair value 0 0
Level III | Restricted deposits | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Assets measured at fair value 0 0
Level III | Restricted deposits | Corporate securities    
Investments:    
Assets measured at fair value 0 0
Level III | Restricted deposits | Municipal securities    
Investments:    
Assets measured at fair value 0 0
Level III | Restricted deposits | Cash and cash equivalents    
Investments:    
Assets measured at fair value 0 0
Level III | Restricted deposits | Certificates of deposit    
Investments:    
Assets measured at fair value 0 $ 0
Level III | Other current assets | Foreign currency swap agreement    
Other current assets:    
Foreign currency swap agreement $ 0