Income Taxes - Quarter End (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Income tax
Net UTB impacting the effective tax rate	$ 375		$ 369
Interest and penalties related to unrecognized tax benefits, expense (benefit) recognized on a gross basis	(4)	$ 2
Interest and penalties related to unrecognized tax benefits, accrued on a gross basis	$ 39		45
Increase (decrease) in effective income tax rate from prior reporting period to current reporting period (as a percent)	(2.70%)
Impact of factors that decreased the effective tax rate from prior reporting period to current reporting period (as a percent)	(5.30%)
Impact of factors that increased the effective tax rate from prior reporting period to current reporting period (as a percent)	2.60%
Deferred Tax Assets, Valuation Allowance	$ 32		$ 31
Reconciliation of Effective Income Tax Rate
Effective tax rate (as a percent)	26.80%	29.50%