Debt - Long-Term Debt Obligations (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018	Apr. 30, 2018	Oct. 31, 2016
Debt Instrument [Line Items]
Total debt	$ 25,411,000,000	$ 24,965,000,000
Less current portion of long-term debt	(2,841,000,000)	(1,371,000,000)
Face value of long-term debt	22,570,000,000	23,594,000,000
Senior Notes
Debt Instrument [Line Items]
Total debt	$ 24,300,000,000
Senior Notes | 2.600% Notes due on December 5, 2019
Debt Instrument [Line Items]
Stated interest rate	2.60%
Total debt	$ 1,000,000,000	1,000,000,000
Effective interest rates	2.73%
Senior Notes | 1.900% Notes due on August 21, 2020
Debt Instrument [Line Items]
Stated interest rate	1.90%
Total debt	$ 1,000,000,000	1,000,000,000
Effective interest rates	2.16%
Senior Notes | 3.300% Notes due on December 5, 2021
Debt Instrument [Line Items]
Stated interest rate	3.30%
Total debt	$ 1,000,000,000	1,000,000,000
Effective interest rates	3.43%
Senior Notes | 2.500% Notes due on November 29, 2022
Debt Instrument [Line Items]
Stated interest rate	2.50%
Total debt	$ 1,250,000,000	1,250,000,000
Effective interest rates	2.66%
Senior Notes | 2.400% Notes due on February 22, 2023
Debt Instrument [Line Items]
Stated interest rate	2.40%
Total debt	$ 1,000,000,000	1,000,000,000
Effective interest rates	2.56%
Senior Notes | 2.800% Notes due on August 22, 2024
Debt Instrument [Line Items]
Stated interest rate	2.80%
Total debt	$ 2,000,000,000	2,000,000,000
Effective interest rates	2.95%
Senior Notes | 3.800% Notes due on December 5, 2024
Debt Instrument [Line Items]
Stated interest rate	3.80%
Total debt	$ 1,250,000,000	1,250,000,000
Effective interest rates	3.90%
Senior Notes | 5.200% Notes due on December 3, 2025
Debt Instrument [Line Items]
Stated interest rate	5.20%
Total debt	$ 1,000,000,000	1,000,000,000
Effective interest rates	3.02%
Senior Notes | 3.150% Notes due on August 22, 2027
Debt Instrument [Line Items]
Stated interest rate	3.15%
Total debt	$ 3,500,000,000	3,500,000,000
Effective interest rates	3.25%
Senior Notes | 4.800% Notes due on December 5, 2034
Debt Instrument [Line Items]
Stated interest rate	4.80%
Total debt	$ 1,250,000,000	1,250,000,000
Effective interest rates	4.92%
Senior Notes | 3.875% Notes due on August 22, 2037
Debt Instrument [Line Items]
Stated interest rate	3.875%
Total debt	$ 2,750,000,000	2,750,000,000
Effective interest rates	3.94%
Senior Notes | 4.950% Notes due on December 5, 2044
Debt Instrument [Line Items]
Stated interest rate	4.95%
Total debt	$ 1,500,000,000	1,500,000,000
Effective interest rates	5.11%
Senior Notes | 4.050% Notes due on August 22, 2047
Debt Instrument [Line Items]
Stated interest rate	4.05%
Total debt	$ 3,500,000,000	3,500,000,000
Effective interest rates	4.13%
Senior Notes | 4.250% Notes due on August 22, 2057
Debt Instrument [Line Items]
Stated interest rate	4.25%
Total debt	$ 2,250,000,000	2,250,000,000
Effective interest rates	4.33%
Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Total debt	$ 603,000,000	594,000,000
Credit Facility | October 2016 Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit maximum borrowing capacity	650,000,000			$ 500,000,000
Credit Facility | April 2018 Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit maximum borrowing capacity			$ 7,000,000,000.0
Other long-term debt
Debt Instrument [Line Items]
Total debt	$ 558,000,000	$ 121,000,000