Total Equity (Preferred Stock Outstanding) (Details) - USD ($) $ / shares in Units, $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Class of Stock
Preferred stock carrying value	$ 7,520	$ 6,020
Series A Preferred Stock
Class of Stock
Preferred stock shares outstanding	44,000
Liquidation preference per share	$ 25,000
Preferred stock carrying value	$ 1,100	1,100
Series C Preferred Stock
Class of Stock
Preferred stock shares outstanding	519,882
Liquidation preference per share	$ 1,000
Preferred stock carrying value	$ 408	408
Series E Preferred Stock
Class of Stock
Preferred stock shares outstanding	34,500
Liquidation preference per share	$ 25,000
Preferred stock carrying value	$ 862	862
Series F Preferred Stock
Class of Stock
Preferred stock shares outstanding	34,000
Liquidation preference per share	$ 25,000
Preferred stock carrying value	$ 850	850
Series G Preferred Stock
Class of Stock
Preferred stock shares outstanding	20,000
Liquidation preference per share	$ 25,000
Preferred stock carrying value	$ 500	500
Series H Preferred Stock
Class of Stock
Preferred stock shares outstanding	52,000
Liquidation preference per share	$ 25,000
Preferred stock carrying value	$ 1,300	1,300
Series I Preferred Stock
Class of Stock
Preferred stock shares outstanding	40,000
Liquidation preference per share	$ 25,000
Preferred stock carrying value	$ 1,000	1,000
Series J Preferred Stock
Class of Stock
Preferred stock shares outstanding	60,000
Liquidation preference per share	$ 25,000
Preferred stock carrying value	$ 1,500	$ 0