Stockholders' Equity - Schedule of Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Dividends Payable [Line Items]
Preferred stock cash dividend	$ 55	$ 41	$ 137	$ 101
Cash dividends declared (in USD per share)	$ 0.38	$ 0.34	$ 1.06	$ 0.98
Common stock dividends	$ 147	$ 138	$ 414	$ 401
Series C Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,313	$ 1,313	$ 3,939	$ 3,939
Preferred stock cash dividend	$ 6	$ 7	$ 19	$ 20
Series C Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.33	$ 0.33	$ 0.99	$ 0.99
Series D Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,475	$ 1,475	$ 4,425	$ 4,425
Preferred stock cash dividend	$ 11	$ 11	$ 33	$ 33
Series D Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.37	$ 0.37	$ 1.11	$ 1.11
Series E Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,500	$ 1,500	$ 4,500	$ 4,833
Preferred stock cash dividend	$ 11	$ 11	$ 33	$ 36
Series E Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.38	$ 0.38	$ 1.14	$ 1.22
Series F Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 2,625	$ 1,663	$ 5,250	$ 1,663
Preferred stock cash dividend	$ 20	$ 12	$ 40	$ 12
Series F Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 26.25	$ 16.63	$ 52.5	$ 16.63
Series G Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,338	$ 0	$ 2,289	$ 0
Preferred stock cash dividend	$ 7	$ 0	$ 12	$ 0
Series G Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.33	$ 0	$ 0.57	$ 0