Shareholders' Equity - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 15, 2020	Dec. 31, 2019	Apr. 30, 2016	May 31, 2015	Feb. 28, 2014
Class of Stock [Line Items]
Preferred stock cash dividend	$ 44	$ 55
Series E Preferred Stock
Class of Stock [Line Items]
Liquidation preference per share (USD per share)			$ 100,000
Preferred stock, shares outstanding (in shares)	7,500			7,500
Preferred dividends declared (USD per share)	$ 0	$ 1,500
Preferred stock cash dividend	$ 0	$ 11
Series E Preferred Stock, Depository Share
Class of Stock [Line Items]
Liquidation preference per share (USD per share)			25.00
Preferred dividends declared (USD per share)	$ 0	$ 0.38
Series C Preferred Stock
Class of Stock [Line Items]
Liquidation preference per share (USD per share)			100,000
Preferred stock, shares outstanding (in shares)	5,000			5,000
Preferred dividends declared (USD per share)	$ 1,313	$ 1,313
Preferred stock cash dividend	$ 6	$ 6
Series C Preferred Stock, Depository Share
Class of Stock [Line Items]
Liquidation preference per share (USD per share)			$ 25.00
Preferred dividends declared (USD per share)	$ 0.33	$ 0.33
Series D Preferred Stock
Class of Stock [Line Items]
Liquidation preference per share (USD per share)							$ 100,000
Preferred stock, shares outstanding (in shares)	7,500			7,500
Preferred dividends declared (USD per share)	$ 1,475	$ 1,475
Preferred stock cash dividend	$ 11	$ 11
Series D Preferred Stock, Depository Share
Class of Stock [Line Items]
Liquidation preference per share (USD per share)							$ 25
Preferred dividends declared (USD per share)	$ 0.37	$ 0.37
Series F Preferred Stock
Class of Stock [Line Items]
Liquidation preference per share (USD per share)						$ 100,000
Preferred stock, shares outstanding (in shares)	7,500			7,500
Preferred dividends declared (USD per share)	$ 2,625	$ 2,625
Preferred stock cash dividend	$ 20	$ 20
Series F Preferred Stock, Depository Share
Class of Stock [Line Items]
Liquidation preference per share (USD per share)						$ 1,000
Preferred dividends declared (USD per share)	$ 26.25	$ 26.25
Series G Preferred Stock
Class of Stock [Line Items]
Liquidation preference per share (USD per share)					$ 100,000
Preferred stock, shares outstanding (in shares)	5,000			5,000
Preferred dividends declared (USD per share)	$ 1,338	$ 1,338
Preferred stock cash dividend	$ 7	$ 7
Series G Preferred Stock, Depository Share
Class of Stock [Line Items]
Liquidation preference per share (USD per share)					$ 25
Preferred dividends declared (USD per share)	$ 0.33	$ 0.33