Shareholders' Equity - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended				6 Months Ended
	Jul. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Mar. 15, 2021	Dec. 31, 2020	Apr. 30, 2016	May 31, 2015	Feb. 28, 2014
Class of Stock [Line Items]
Preferred stock cash dividend		$ 34	$ 25	$ 32	$ 44	$ 59	$ 76
Series F Preferred Stock
Class of Stock [Line Items]
Redemption price								$ 500
Preferred shares to be redeemed (in shares)								5,000
Preferred stock, shares outstanding (in shares)		2,500				2,500		7,500	2,500
Liquidation preference per share (USD per share)								$ 100,000			$ 100,000
Preferred dividends declared (USD per share)		$ 966		$ 0		$ 1,919	$ 2,625
Preferred stock cash dividend		$ 2		$ 0		$ 9	$ 20
Series F Preferred Stock | Subsequent Event | Forecast
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 950
Preferred stock cash dividend	$ 2
Series F Preferred Stock, Depository Share
Class of Stock [Line Items]
Liquidation preference per share (USD per share)								$ 1,000			$ 1,000
Preferred dividends declared (USD per share)		$ 9.66		$ 0		$ 19.19	$ 26.25
Series F Preferred Stock, Depository Share | Subsequent Event | Forecast
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 9.50
Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)		7,500				7,500			7,500
Liquidation preference per share (USD per share)												$ 100,000
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 | Subsequent Event | Forecast
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 1,475
Preferred stock cash dividend	$ 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		$ 0.74	$ 0.74
Series D Preferred Stock, Depository Share | Subsequent Event | Forecast
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 0.37
Series G Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)		5,000				5,000			5,000
Liquidation preference per share (USD per share)										$ 100,000
Preferred dividends declared (USD per share)		$ 1,338		$ 1,338		$ 2,676	$ 2,676,000,000
Preferred stock cash dividend		$ 7		$ 7		$ 14	$ 14
Series G Preferred Stock | Subsequent Event | Forecast
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 1,338
Preferred stock cash dividend	$ 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		$ 0.66	$ 0.66
Series G Preferred Stock, Depository Share | Subsequent Event | Forecast
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 0.33