Debt and Lines of Credit - Additional Information (Details) - USD ($)	1 Months Ended						12 Months Ended
	May 31, 2016	Aug. 31, 2015	May 31, 2015	Apr. 30, 2015	May 31, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Commercial paper							$ 0
Long-term debt, gross							3,625,000,000	$ 4,125,000,000
Proceeds from issuance of long-term debt							499,000,000	498,000,000	$ 498,000,000
Interest and debt expense							80,000,000	90,000,000	94,000,000
Interest paid							88,000,000	99,000,000	$ 102,000,000
Notes payable
Debt Instrument [Line Items]
Long-term debt, gross						$ 500,000,000
Payments of debt issuance costs						3,000,000
Proceeds from issuance of long-term debt						498,000,000
Retirement of long-term debt	$ 1,000,000,000	$ 750,000,000		$ 250,000,000	$ 1,000,000,000
Consortium of investment-grade banks | Revolving credit facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity until March 2021							2,000,000,000
Notes due 2022 at 1.85%
Debt Instrument [Line Items]
Long-term debt, gross	500,000,000						500,000,000	0
Payments of debt issuance costs	3,000,000
Proceeds from issuance of long-term debt	$ 499,000,000
Notes due 2020 at 1.75%
Debt Instrument [Line Items]
Long-term debt, gross			$ 500,000,000				500,000,000	500,000,000
Payments of debt issuance costs			3,000,000
Proceeds from issuance of long-term debt			$ 498,000,000
Notes due 2017 at 0.875%
Debt Instrument [Line Items]
Long-term debt, gross						250,000,000	250,000,000	250,000,000
Notes due 2021 at 2.75%
Debt Instrument [Line Items]
Long-term debt, gross						$ 250,000,000	$ 250,000,000	$ 250,000,000