Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Income tax
Net UTB impacting the effective tax rate	$ 279		$ 279		$ 265
Interest and penalties related to unrecognized tax benefits, expense (benefit) recognized on a gross basis	5	$ (1)	3	$ (14)
Interest and penalties related to unrecognized tax benefits, accrued on a gross basis	$ 46		$ 46		44
Increase (decrease) in effective income tax rate from prior reporting period to current reporting period (as a percent)	(0.70%)
Impact of factors that decreased the effective tax rate from prior reporting period to current reporting period (as a percent)	3.10%		1.20%
Impact of factors that increased the effective tax rate from prior reporting period to current reporting period (as a percent)	2.40%		1.20%
Deferred tax assets valuation allowance	$ 37		$ 37		$ 22
Reconciliation of Effective Income Tax Rate
Effective tax rate (as a percent)	29.60%	30.30%	29.10%	29.10%