Shareholders' Equity - Schedule of Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Feb. 28, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Dividends Payable [Line Items]
Preferred stock cash dividend		$ 182	$ 173	$ 130
Common Stock Dividends Declared (in USD per share)		$ 1.6	$ 1.44	$ 1.32
Common Stock Dividends		$ 596	$ 559	$ 536
Series C Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 5,250	$ 5,250
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	$ 5,900
Preferred stock cash dividend		$ 44	$ 44
Series D Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 1.48	$ 1.48
Series E Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 6,000	$ 6,000
Preferred stock cash dividend		$ 45	$ 45
Series E Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 1.52	$ 1.52
Series F Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 5,250	$ 5,250
Preferred stock cash dividend		$ 40	$ 40
Series F Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 52.5	$ 52.50
Series G Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 5,352	$ 3,626
Preferred stock cash dividend		$ 27	$ 18
Series G Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)		$ 1.32	$ 0.90
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 F Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 2,625
Preferred stock cash dividend	$ 20
Subsequent Event | Series F Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 26.25
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