Background and Basis of Presentation (Share Repurchase Table) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Repurchase of common stock, shares	2.8	3.6
Repurchases of common stock, value	$ 168	$ 192	$ 554
Average price of repurchased shares, per share	$ 59.81	$ 53.03