Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 47	$ 46	$ 88	$ 86
Tax expense for prior year tax adjustments	2		3
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount				$ 1
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Other Information	$ 6		$ 6