Stockholders' Equity - Schedule of Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Dividends Payable [Line Items]
Preferred stock cash dividend	$ 33	$ 29	$ 82	$ 60
Cash dividends declared (in USD per share)	$ 0.34	$ 0.34	$ 0.68	$ 0.64
Common stock dividends	$ 133	$ 139	$ 268	$ 262
Series C Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,313	$ 1,313	$ 2,626	$ 2,626
Preferred stock cash dividend	$ 6	$ 7	$ 13	$ 13
Series C Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.33	$ 0.33	$ 0.66	$ 0.66
Series D Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,475	$ 1,475	$ 2,950	$ 2,950
Preferred stock cash dividend	$ 11	$ 11	$ 22	$ 22
Series D Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.37	$ 0.37	$ 0.74	$ 0.74
Series E Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,500	$ 1,500	$ 3,000	$ 3,333
Preferred stock cash dividend	$ 11	$ 11	$ 22	$ 25
Series E Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.38	$ 0.38	$ 0.76	$ 0.84
Series F Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0	$ 0	$ 2,625	$ 0
Preferred stock cash dividend	$ 0	$ 0	$ 20	$ 0
Series F Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0	$ 0	$ 26.25	$ 0
Series G Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 951	$ 0	$ 951	$ 0
Preferred stock cash dividend	$ 5	$ 0	$ 5	$ 0
Series G Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.24	$ 0	$ 0.24	$ 0