Shareholders' Equity - Preferred Stock (Details) - USD ($)		1 Months Ended		3 Months Ended	12 Months Ended
	Jan. 14, 2021	Mar. 31, 2021	Feb. 28, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 15, 2020	Sep. 30, 2019	Apr. 30, 2016	May 31, 2015	Feb. 28, 2014
Class of Stock [Line Items]
Preferred stock cash dividend					$ 152,000,000	$ 210,000,000	$ 188,000,000
Series C Preferred Stock
Class of Stock [Line Items]
Redemption price								$ 500,000,000
Liquidation preference per share (USD per share)								$ 100,000
Preferred stock, shares outstanding (in shares)					5,000
Preferred dividends declared (USD per share)					$ 1,313	$ 5,250
Preferred stock cash dividend					$ 6,000,000	$ 26,000,000
Series C Preferred Stock, Depository Share
Class of Stock [Line Items]
Liquidation preference per share (USD per share)								$ 25.00
Premium from difference between redemption value and net carrying value				$ 9,000,000
Premium EPS impact (in USD per share)				$ (0.03)
Preferred dividends declared (USD per share)					$ 0.33	$ 1.32
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)					$ 1.48	1.48
Series D Preferred Stock, Depository Share | Subsequent Event
Class of Stock [Line Items]
Preferred dividends declared (USD per share)			$ 0.37
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
Preferred dividends declared (USD per share)					$ 5,900	$ 5,900
Preferred stock cash dividend					$ 44,000,000	$ 44,000,000
Series D Preferred Stock | Subsequent Event
Class of Stock [Line Items]
Preferred dividends declared (USD per share)			1,475
Preferred stock cash dividend		$ 11,000,000
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)					$ 62.23	$ 52.50
Series F Preferred Stock, Depository Share | Subsequent Event
Class of Stock [Line Items]
Liquidation preference per share (USD per share)	$ 1,000
Preferred dividends declared (USD per share)			9.53
Preferred stock cash dividend	$ 9.5338
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
Preferred dividends declared (USD per share)					$ 6,223	$ 5,250
Preferred stock cash dividend					$ 47,000,000	$ 40,000,000
Series F Preferred Stock | Subsequent Event
Class of Stock [Line Items]
Redemption price	$ 500,000,000
Liquidation preference per share (USD per share)	$ 100,000
Preferred shares to be redeemed (in shares)	5,000
Preferred stock, shares outstanding (in shares)	7,500
Preferred dividends declared (USD per share)			953
Preferred stock cash dividend	$ 953.38	7,000,000
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)					$ 1.32	$ 1.32
Series G Preferred Stock, Depository Share | Subsequent Event
Class of Stock [Line Items]
Preferred dividends declared (USD per share)			0.33
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
Preferred dividends declared (USD per share)					$ 5,352	$ 5,352
Preferred stock cash dividend					$ 27,000,000	$ 27,000,000
Series G Preferred Stock | Subsequent Event
Class of Stock [Line Items]
Preferred dividends declared (USD per share)			$ 1,338
Preferred stock cash dividend		$ 7,000,000
Series H Preferred Stock, Depository Share
Class of Stock [Line Items]
Liquidation preference per share (USD per share)									$ 1,000
Preferred dividends declared (USD per share)					$ 56.25	$ 56.25
Series H Preferred Stock
Class of Stock [Line Items]
Liquidation preference per share (USD per share)									$ 100,000
Preferred stock, shares outstanding (in shares)					5,000
Preferred dividends declared (USD per share)					$ 5,625	$ 5,625
Preferred stock cash dividend					$ 28,000,000	$ 28,000,000