Background and Basis of Presentation (Share Repurchase Programs) (Details) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended		9 Months Ended		12 Months Ended	15 Months Ended	18 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Sep. 30, 2015	Sep. 30, 2014	Jul. 31, 2015	Jul. 31, 2014	Aug. 31, 2013	Apr. 30, 2013
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock, shares	1.2	6.4	10.0	17.2
Repurchases of common stock, value	$ 63,000,000	$ 275,000,000	$ 518,000,000	$ 679,000,000	$ 939,000,000
Average price of repurchased shares, per share	$ 50.39	$ 42.87	$ 51.47	$ 39.44
April 2013 Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Planned share repurchase program										$ 1,000,000,000	$ 300,000,000
Repurchase of common stock, shares							27.1
Average price of repurchased shares, per share							$ 36.97
July 2014 Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Planned share repurchase program									$ 1,000,000,000
Repurchase of common stock, shares	1.2					20.4
Repurchases of common stock, value	$ 63,000,000
Average price of repurchased shares, per share	$ 50.39					$ 48.90
July 2015 Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Planned share repurchase program								$ 1,000,000,000