Debt (details) - Debt Issuance - USD ($) $ in Millions			12 Months Ended
	Aug. 25, 2015	Jul. 25, 2013	Dec. 31, 2015	Dec. 31, 2013
Debt Instrument
Net proceeds of issuance, after original issuance discount and deduction of underwriting expenses and commissions and other expenses			$ 392	$ 494
Senior notes [Member]
Debt Instrument
Debt, principal amount	$ 400	$ 500
Interest rate (percent)	4.30%	4.60%
Net proceeds of issuance, after original issuance discount and deduction of underwriting expenses and commissions and other expenses	$ 392	$ 494
Percentage of principal amount at which redemption price may be set	100.00%	100.00%
Basis points added to current treasury rate used in calculation of alternative redemption price	0.25%	0.15%