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Debt - Schedule of Debt (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016	Sep. 22, 2016	May 26, 2015
Debt Instrument [Line Items]
Total debt	$ 3,568,000,000	$ 3,564,000,000
Less: short-term debt including current maturities	0	0
Long-term debt	3,568,000,000	3,564,000,000
Commercial paper \| Five-Year Credit Agreement
Debt Instrument [Line Items]
Short-term debt	$ 0	0
Senior notes \| 2.5% Senior Notes, due 2018
Debt Instrument [Line Items]
Stated interest rate	2.50%
Long-term debt	$ 399,000,000	398,000,000
Unamortized debt discount and issuance costs	$ 1,000,000
Senior notes \| 3.3% Senior Notes, due 2020
Debt Instrument [Line Items]
Stated interest rate	3.30%
Long-term debt	$ 697,000,000	696,000,000
Unamortized debt discount and issuance costs	$ 3,000,000
Senior notes \| 4.0% Senior Notes, due 2025
Debt Instrument [Line Items]
Stated interest rate	4.00%			4.00%
Long-term debt	$ 692,000,000	691,000,000
Unamortized debt discount and issuance costs	$ 8,000,000
Senior notes \| 4.4% Senior Notes, due 2026
Debt Instrument [Line Items]
Stated interest rate	4.40%
Long-term debt	$ 892,000,000	891,000,000
Unamortized debt discount and issuance costs	$ 8,000,000
Senior notes \| 2.95% Senior Notes, due 2027
Debt Instrument [Line Items]
Stated interest rate	2.95%		2.95%
Long-term debt	$ 492,000,000	492,000,000
Unamortized debt discount and issuance costs	$ 8,000,000
Senior notes \| 6.55% Senior Notes, due 2037
Debt Instrument [Line Items]
Stated interest rate	6.55%
Long-term debt	$ 396,000,000	$ 396,000,000
Unamortized debt discount and issuance costs	$ 4,000,000