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, 2017	Mar. 31, 2016	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Repurchase of common stock (shares)	7.7	2.8
Aggregate cost of shares repurchased	$ 551	$ 168	$ 1,030
Average price of repurchased shares, per share (usd per share)	$ 71.77	$ 59.81