Equity Equity (Dividends) (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	2 Months Ended	3 Months Ended								12 Months Ended			66 Months Ended	68 Months Ended
	Dec. 11, 2015	Oct. 31, 2015	Feb. 23, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Feb. 23, 2016
Subsequent Event [Line Items]
Common Stock, Dividends, Per Share, Cash Paid				$ 0.10	$ 0.1	$ 0.1	$ 0.10	$ 0.05	$ 0.05	$ 0.05	$ 0.05
Dividends declared on common stock (per share amount)	$ 0.11			$ 0.21	$ 0.1	$ 0.1	$ 0	$ 0.15	$ 0.05	$ 0.05	$ 0	$ 0.41	$ 0.25	$ 0.17
Stock repurchase program, additional authorized amount		$ 400
Treasury Stock, Value, Acquired, Cost Method												$ 0		$ 0	$ 1,800
Payments for Repurchase of Common Stock												$ 482	$ 308	$ 322
Acquisition of treasury stock (shares)												39,700,000			145,600,000
Treasury Stock Acquired, Average Cost Per Share															$ 12.31
Stock Repurchase Program, Remaining Authorized Repurchase Amount				$ 343								$ 343			$ 343
Treasury stock, shares (in shares)				149,037,831				110,687,849				149,037,831	110,687,849		149,037,831
Stock Repurchase Program, Authorized Amount				$ 2,100								$ 2,100			$ 2,100
Subsequent Event
Subsequent Event [Line Items]
Treasury Stock, Value, Acquired, Cost Method			$ 79													$ 1,900
Acquisition of treasury stock (shares)			8,700,000													154,300,000
Treasury Stock Acquired, Average Cost Per Share																$ 12.12
Stock Repurchase Program, Remaining Authorized Repurchase Amount			$ 264													$ 264