Stockholders' Equity - Schedule of Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Dividends Payable [Line Items]
Cash dividends declared (USD per share)	$ 1.32	$ 1.16	$ 1.04
Common stock dividends	$ 536	$ 490	$ 463
Preferred stock cash dividend	$ 130	$ 61
Series C Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 5,250	$ 5,252
Preferred stock cash dividend	$ 26	$ 26
Series C Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1.32	$ 1.32
Series D Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 5,900	$ 4,605
Preferred stock cash dividend	$ 44	$ 35
Series D Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1.48	$ 1.15
Series E Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 6,333	$ 0
Preferred stock cash dividend	$ 48	$ 0
Series E Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1.6	$ 0
Series F Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,663	$ 0
Preferred stock cash dividend	$ 12	$ 0
Series F Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 16.63	$ 0