Shareholders' Equity - Schedule of Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Dividends Payable [Line Items]
Preferred stock cash dividend	$ 50	$ 55	$ 36	$ 55	$ 105	$ 91
Cash dividends declared (in USD per share)	$ 0.47	$ 0.47	$ 0.42	$ 0.42	$ 0.94	$ 0.84
Common stock dividends	$ 175	$ 177	$ 153	$ 154	$ 352	$ 307
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
Series H Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 2,813		$ 0		$ 2,813	$ 0
Preferred stock cash dividend	$ 14		$ 0		$ 14	$ 0
Series H Preferred Stock, Depository Share
Dividends Payable [Line Items]
Preferred dividends declared (USD per share)	$ 28.13		$ 0		$ 28.13	$ 0