Background and Basis of Presentation (Share Repurchase Table) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Equity, Class of Treasury Stock [Line Items]
Aggregate cost of shares repurchased			$ 2,359		$ 1,030
July 2015 Share Repurcahse Program [Member]
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock (shares)	11.1	2.6	33.2	8.1
Aggregate cost of shares repurchased	$ 759	$ 171	$ 2,359	$ 512
Average price of repurchased shares, per share (usd per share)	$ 67.99	$ 66.23	$ 70.97	$ 63.28