Shareholders' Equity - Schedule of Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Dividends Payable [Line Items]
Preferred stock cash dividend	$ 36	$ 36	$ 91	$ 91
Common Stock Dividends Declared (in USD per share)	$ 0.42	$ 0.38	$ 0.84	$ 0.76
Common Stock Dividends	$ 153	$ 142	$ 307	$ 286
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	$ 7	$ 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	$ 3,000
Preferred stock cash dividend	$ 11	$ 11	$ 22	$ 22
Series E Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.38	$ 0.38	$ 0.76	$ 0.76
Series F Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0	$ 0	$ 2,625	$ 2,625
Preferred stock cash dividend	$ 0	$ 0	$ 20	$ 20
Series F Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0	$ 0	$ 26.25	$ 26.25
Series G Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,338	$ 1,338	$ 2,676	$ 2,676
Preferred stock cash dividend	$ 7	$ 7	$ 14	$ 14
Series G Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.33	$ 0.33	$ 0.66	$ 0.66