Shareholders' Equity - Schedule of Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended
	Apr. 30, 2017	Mar. 31, 2017	Mar. 31, 2016
Dividends Payable [Line Items]
Preferred stock cash dividend		$ 55	$ 49
Common Stock Dividends Declared (in USD per share)		$ 0.38	$ 0.34
Common Stock Dividends		$ 144	$ 135
Series C Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 1,313	$ 1,313
Preferred stock cash dividend		$ 6	$ 7
Series C Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 0.33	$ 0.33
Series D Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 1,475	$ 1,475
Preferred stock cash dividend		$ 11	$ 11
Series D Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 0.37	$ 0.37
Series E Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 1,500	$ 1,500
Preferred stock cash dividend		$ 11	$ 11
Series E Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 0.38	$ 0.38
Series F Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 2,625	$ 2,625
Preferred stock cash dividend		$ 20	$ 20
Series F Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 26.25	$ 26.25
Series G Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 1,338	$ 0
Preferred stock cash dividend		$ 7	$ 0
Series G Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 0.33	$ 0
Subsequent Event | Series C Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,313
Preferred stock cash dividend	$ 6
Subsequent Event | Series C Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.33
Subsequent Event | Series D Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,475
Preferred stock cash dividend	$ 11
Subsequent Event | Series D Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.37
Subsequent Event | Series E Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,500
Preferred stock cash dividend	$ 11
Subsequent Event | Series E Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.38
Subsequent Event | Series G Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 1,338
Preferred stock cash dividend	$ 7
Subsequent Event | Series G Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 0.33