Long-Term Debt - Long-Term Debt Obligations (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total debt	$ 8,832	$ 8,838
Less current portion of long-term debt	(1,063)	(1,056)
Face value of long-term debt	7,769	7,782
Senior Notes
Debt Instrument [Line Items]
Total debt	$ 8,300
Senior Notes | 1.20% Notes due on November 29, 2017
Debt Instrument [Line Items]
Stated interest rate	1.20%
Total debt	$ 1,000	1,000
Effective interest rates	1.38%
Senior Notes | 2.60% Notes due on December 5, 2019
Debt Instrument [Line Items]
Stated interest rate	2.60%
Total debt	$ 1,000	1,000
Effective interest rates	2.73%
Senior Notes | 3.30% Notes due on December 5, 2021
Debt Instrument [Line Items]
Stated interest rate	3.30%
Total debt	$ 1,000	1,000
Effective interest rates	3.43%
Senior Notes | 2.50% Notes due on November 29, 2022
Debt Instrument [Line Items]
Stated interest rate	2.50%
Total debt	$ 1,250	1,250
Effective interest rates	2.66%
Senior Notes | 3.80% Notes due on December 5, 2024
Debt Instrument [Line Items]
Stated interest rate	3.80%
Total debt	$ 1,250	1,250
Effective interest rates	3.90%
Senior Notes | 4.80% Notes due on December 5, 2034
Debt Instrument [Line Items]
Stated interest rate	4.80%
Total debt	$ 1,250	1,250
Effective interest rates	4.92%
Senior Notes | 4.95% Notes due on December 5, 2044
Debt Instrument [Line Items]
Stated interest rate	4.95%
Total debt	$ 1,500	1,500
Effective interest rates	5.11%
Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Total debt	$ 500	495
Other Long-term Debt
Debt Instrument [Line Items]
Total debt	$ 82	$ 93