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
Mar. 31, 2020
Dec. 31, 2019
Assets    
Cash and cash equivalents $ 9,308 $ 12,123
Investments:    
Equity securities 685 0
Other long-term assets:    
Total assets at fair value 21,351 20,559
Other long-term liabilities:    
Total liabilities at fair value   11
U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 778 212
Corporate securities    
Investments:    
Fair Value 4,978 3,733
Municipal securities    
Investments:    
Fair Value 2,584 2,388
Short-term time deposits    
Investments:    
Fair Value 84 0
Asset-backed securities    
Investments:    
Fair Value 1,018 744
Residential mortgage-backed securities    
Investments:    
Fair Value 1,027 471
Commercial mortgage-backed securities    
Investments:    
Fair Value 587 388
Interest rate swap agreements    
Other long-term liabilities:    
Interest rate swap agreements   11
Available-for-sale Securities    
Investments:    
Fair Value 11,029 7,768
Available-for-sale Securities | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 114 73
Available-for-sale Securities | Corporate securities    
Investments:    
Fair Value 4,960 3,713
Available-for-sale Securities | Municipal securities    
Investments:    
Fair Value 2,554 2,379
Available-for-sale Securities | Short-term time deposits    
Investments:    
Fair Value 84  
Available-for-sale Securities | Asset-backed securities    
Investments:    
Fair Value 1,018 744
Available-for-sale Securities | Residential mortgage-backed securities    
Investments:    
Fair Value 1,027 471
Available-for-sale Securities | Commercial mortgage-backed securities    
Investments:    
Fair Value 587 388
Restricted Deposits    
Investments:    
Fair Value 1,014 658
Restricted Deposits | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 664 139
Restricted Deposits | Corporate securities    
Investments:    
Fair Value 18 20
Restricted Deposits | Municipal securities    
Investments:    
Fair Value 30 9
Restricted Deposits | Cash and cash equivalents    
Investments:    
Fair Value 149 8
Restricted Deposits | Certificates of deposit    
Investments:    
Fair Value 153 482
Other long-term assets | Interest rate swap agreements    
Other long-term assets:    
Derivative asset   10
Level I    
Assets    
Cash and cash equivalents 9,308 12,123
Investments:    
Equity securities 683  
Other long-term assets:    
Total assets at fair value 10,918 12,343
Other long-term liabilities:    
Total liabilities at fair value   0
Level I | Interest rate swap agreements    
Other long-term liabilities:    
Interest rate swap agreements   0
Level I | Available-for-sale Securities    
Investments:    
Fair Value 797 73
Level I | Available-for-sale Securities | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 114 73
Level I | Available-for-sale Securities | Corporate securities    
Investments:    
Fair Value 0 0
Level I | Available-for-sale Securities | Municipal securities    
Investments:    
Fair Value 0 0
Level I | Available-for-sale Securities | Short-term time deposits    
Investments:    
Fair Value 0  
Level I | Available-for-sale Securities | Asset-backed securities    
Investments:    
Fair Value 0 0
Level I | Available-for-sale Securities | Residential mortgage-backed securities    
Investments:    
Fair Value 0 0
Level I | Available-for-sale Securities | Commercial mortgage-backed securities    
Investments:    
Fair Value 0 0
Level I | Restricted Deposits    
Investments:    
Fair Value 813 147
Level I | Restricted Deposits | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 664 139
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 149 8
Level I | Restricted Deposits | Certificates of deposit    
Investments:    
Fair Value 0 0
Level I | Other long-term assets | Interest rate swap agreements    
Other long-term assets:    
Derivative asset   0
Level II    
Assets    
Cash and cash equivalents 0 0
Investments:    
Equity securities 2  
Other long-term assets:    
Total assets at fair value 10,433 8,216
Other long-term liabilities:    
Total liabilities at fair value   11
Level II | Interest rate swap agreements    
Other long-term liabilities:    
Interest rate swap agreements   11
Level II | Available-for-sale Securities    
Investments:    
Fair Value 10,232 7,695
Level II | Available-for-sale Securities | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 0 0
Level II | Available-for-sale Securities | Corporate securities    
Investments:    
Fair Value 4,960 3,713
Level II | Available-for-sale Securities | Municipal securities    
Investments:    
Fair Value 2,554 2,379
Level II | Available-for-sale Securities | Short-term time deposits    
Investments:    
Fair Value 84  
Level II | Available-for-sale Securities | Asset-backed securities    
Investments:    
Fair Value 1,018 744
Level II | Available-for-sale Securities | Residential mortgage-backed securities    
Investments:    
Fair Value 1,027 471
Level II | Available-for-sale Securities | Commercial mortgage-backed securities    
Investments:    
Fair Value 587 388
Level II | Restricted Deposits    
Investments:    
Fair Value 201 511
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 18 20
Level II | Restricted Deposits | Municipal securities    
Investments:    
Fair Value 30 9
Level II | Restricted Deposits | Cash and cash equivalents    
Investments:    
Fair Value 0 0
Level II | Restricted Deposits | Certificates of deposit    
Investments:    
Fair Value 153 482
Level II | Other long-term assets | Interest rate swap agreements    
Other long-term assets:    
Derivative asset   10
Level III    
Assets    
Cash and cash equivalents 0 0
Investments:    
Equity securities 0  
Other long-term assets:    
Total assets at fair value 0 0
Other long-term liabilities:    
Total liabilities at fair value   0
Level III | Interest rate swap agreements    
Other long-term liabilities:    
Interest rate swap agreements   0
Level III | Available-for-sale Securities    
Investments:    
Fair Value 0 0
Level III | Available-for-sale Securities | U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Investments:    
Fair Value 0 0
Level III | Available-for-sale Securities | Corporate securities    
Investments:    
Fair Value 0 0
Level III | Available-for-sale Securities | Municipal securities    
Investments:    
Fair Value 0 0
Level III | Available-for-sale Securities | Short-term time deposits    
Investments:    
Fair Value 0  
Level III | Available-for-sale Securities | Asset-backed securities    
Investments:    
Fair Value 0 0
Level III | Available-for-sale Securities | Residential mortgage-backed securities    
Investments:    
Fair Value 0 0
Level III | Available-for-sale Securities | 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    
Other long-term assets:    
Derivative asset   $ 0