Subsequent Event (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2015	Sep. 30, 2014
Subsequent Event [Line Items]
Amount of common stock agreed to repurchase	$ 1,500	$ 2,500	$ 1,700	$ 2,025	$ 4,238
Immediate delivery of stock (in shares)	19,600,000.0	23,700,000.0	18,110,735	25,841,608	41,762,325