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
Jun. 30, 2022
Dec. 31, 2021
Assets    
Cash and cash equivalents $ 13,435 $ 13,118
Investments:    
Equity securities 70 326
Total assets at fair value 29,389 29,010
U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 706 640
Corporate securities    
Investments:    
Fair Value 8,372 8,200
Municipal securities    
Investments:    
Fair Value 3,529 3,468
Short-term time deposits    
Investments:    
Fair Value 88 109
Asset-backed securities    
Investments:    
Fair Value 1,270 1,308
Residential mortgage-backed securities    
Investments:    
Fair Value 916 853
Commercial mortgage-backed securities    
Investments:    
Fair Value 853 873
Investments available-for-sale    
Investments:    
Fair Value 14,729 14,809
Investments available-for-sale | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 239 171
Investments available-for-sale | Corporate securities    
Investments:    
Fair Value 8,341 8,170
Investments available-for-sale | Municipal securities    
Investments:    
Fair Value 2,952 2,999
Investments available-for-sale | Short-term time deposits    
Investments:    
Fair Value 88 109
Investments available-for-sale | Asset-backed securities    
Investments:    
Fair Value 1,270 1,308
Investments available-for-sale | Residential mortgage-backed securities    
Investments:    
Fair Value 916 853
Investments available-for-sale | Commercial mortgage-backed securities    
Investments:    
Fair Value 853 873
Restricted deposits    
Investments:    
Fair Value 1,225 1,068
Restricted deposits | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 467 469
Restricted deposits | Corporate securities    
Investments:    
Fair Value 31 30
Restricted deposits | Municipal securities    
Investments:    
Fair Value 577 469
Restricted deposits | Cash and cash equivalents    
Investments:    
Fair Value 146 96
Restricted deposits | Certificates of deposit    
Investments:    
Fair Value 4 4
Other long-term assets: | Interest rate swap agreements    
Investments:    
Derivative asset   15
Level I    
Assets    
Cash and cash equivalents 13,435 13,118
Investments:    
Equity securities 68 324
Total assets at fair value 14,355 14,178
Level I | Investments available-for-sale    
Investments:    
Fair Value 307 495
Level I | Investments available-for-sale | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 239 171
Level I | Investments available-for-sale | Corporate securities    
Investments:    
Fair Value 0 0
Level I | Investments available-for-sale | Municipal securities    
Investments:    
Fair Value 0 0
Level I | Investments available-for-sale | Short-term time deposits    
Investments:    
Fair Value 0 0
Level I | Investments available-for-sale | Asset-backed securities    
Investments:    
Fair Value 0 0
Level I | Investments available-for-sale | Residential mortgage-backed securities    
Investments:    
Fair Value 0 0
Level I | Investments available-for-sale | Commercial mortgage-backed securities    
Investments:    
Fair Value 0 0
Level I | Restricted deposits    
Investments:    
Fair Value 613 565
Level I | Restricted deposits | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 467 469
Level I | Restricted deposits | Corporate securities    
Investments:    
Fair Value 0 0
Level I | Restricted deposits | Municipal securities    
Investments:    
Fair Value 0 0
Level I | Restricted deposits | Cash and cash equivalents    
Investments:    
Fair Value 146 96
Level I | Restricted deposits | Certificates of deposit    
Investments:    
Fair Value 0 0
Level I | Other long-term assets: | Interest rate swap agreements    
Investments:    
Derivative asset   0
Level II    
Assets    
Cash and cash equivalents 0 0
Investments:    
Equity securities 2 2
Total assets at fair value 15,034 14,832
Level II | Investments available-for-sale    
Investments:    
Fair Value 14,422 14,314
Level II | Investments available-for-sale | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 0 0
Level II | Investments available-for-sale | Corporate securities    
Investments:    
Fair Value 8,341 8,170
Level II | Investments available-for-sale | Municipal securities    
Investments:    
Fair Value 2,952 2,999
Level II | Investments available-for-sale | Short-term time deposits    
Investments:    
Fair Value 88 109
Level II | Investments available-for-sale | Asset-backed securities    
Investments:    
Fair Value 1,270 1,308
Level II | Investments available-for-sale | Residential mortgage-backed securities    
Investments:    
Fair Value 916 853
Level II | Investments available-for-sale | Commercial mortgage-backed securities    
Investments:    
Fair Value 853 873
Level II | Restricted deposits    
Investments:    
Fair Value 612 503
Level II | Restricted deposits | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 0 0
Level II | Restricted deposits | Corporate securities    
Investments:    
Fair Value 31 30
Level II | Restricted deposits | Municipal securities    
Investments:    
Fair Value 577 469
Level II | Restricted deposits | Cash and cash equivalents    
Investments:    
Fair Value 0 0
Level II | Restricted deposits | Certificates of deposit    
Investments:    
Fair Value 4 4
Level II | Other long-term assets: | Interest rate swap agreements    
Investments:    
Derivative asset   15
Level III    
Assets    
Cash and cash equivalents 0 0
Investments:    
Equity securities 0 0
Total assets at fair value 0 0
Level III | Investments available-for-sale    
Investments:    
Fair Value 0 0
Level III | Investments available-for-sale | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 0 0
Level III | Investments available-for-sale | Corporate securities    
Investments:    
Fair Value 0 0
Level III | Investments available-for-sale | Municipal securities    
Investments:    
Fair Value 0 0
Level III | Investments available-for-sale | Short-term time deposits    
Investments:    
Fair Value 0 0
Level III | Investments available-for-sale | Asset-backed securities    
Investments:    
Fair Value 0 0
Level III | Investments available-for-sale | Residential mortgage-backed securities    
Investments:    
Fair Value 0 0
Level III | Investments available-for-sale | Commercial mortgage-backed securities    
Investments:    
Fair Value 0 0
Level III | Restricted deposits    
Investments:    
Fair Value 0 0
Level III | Restricted deposits | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 0 0
Level III | Restricted deposits | Corporate securities    
Investments:    
Fair Value 0 0
Level III | Restricted deposits | Municipal securities    
Investments:    
Fair Value 0 0
Level III | Restricted deposits | Cash and cash equivalents    
Investments:    
Fair Value 0 0
Level III | Restricted deposits | Certificates of deposit    
Investments:    
Fair Value $ 0 0
Level III | Other long-term assets: | Interest rate swap agreements    
Investments:    
Derivative asset   $ 0