Debt (details) - USD ($) $ in Millions		9 Months Ended
	May 11, 2016	Sep. 30, 2016	Sep. 30, 2015
Debt Instrument
Net proceeds of issuance, after the deduction of underwriting and other expenses		$ 491	$ 392
Senior notes [Member]
Debt Instrument
Debt, principal amount	$ 500
Interest rate (percent)	3.75%
Net proceeds of issuance, after the deduction of underwriting and other expenses	$ 491
Percentage of principal amount at which redemption price may be set	100.00%
Basis points added to current treasury rate used in calculation of alternative redemption price	0.20%