Shareholders' Equity - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Mar. 15, 2020	Dec. 31, 2019	Dec. 15, 2019	Apr. 30, 2016	May 31, 2015	Feb. 28, 2014
Class of Stock [Line Items]
Preferred stock cash dividend	$ 38	$ 32	$ 44	$ 55	$ 50	$ 55	$ 114	$ 160
Series E Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 0			$ 1,500			$ 0	$ 4,500
Preferred stock cash dividend	$ 0			$ 11			$ 0	$ 33
Liquidation preference per share (USD per share)											$ 100,000
Series E Preferred Stock, Depository Share
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 0			$ 0.38			$ 0	$ 1.14
Liquidation preference per share (USD per share)									$ 25.00
Series C Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 0			$ 1,313			$ 1,313	$ 3,939
Preferred stock cash dividend	$ 0			$ 6			$ 6	$ 19
Liquidation preference per share (USD per share)									100,000
Preferred stock, shares outstanding (in shares)	5,000						5,000			5,000
Series C Preferred Stock, Depository Share
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 0			$ 0.33			$ 0.33	$ 0.99
Liquidation preference per share (USD per share)									$ 25.00
Series D Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 1,475			$ 1,475			$ 4,425	$ 4,425
Preferred stock cash dividend	$ 11			$ 11			$ 33	$ 33
Liquidation preference per share (USD per share)														$ 100,000
Preferred stock, shares outstanding (in shares)	7,500						7,500			7,500
Series D Preferred Stock, Depository Share
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 0.37			$ 0.37			$ 1.11	$ 1.11
Liquidation preference per share (USD per share)														$ 25
Series F Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 2,625			$ 2,625			$ 5,250	$ 5,250
Preferred stock cash dividend	$ 20			$ 20			$ 40	$ 40
Liquidation preference per share (USD per share)													$ 100,000
Preferred stock, shares outstanding (in shares)	7,500						7,500			7,500
Series F Preferred Stock, Depository Share
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 26.25			$ 26.25			$ 52.50	$ 52.50
Liquidation preference per share (USD per share)													$ 1,000
Series G Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 1,338			$ 1,338			$ 4,014	$ 4,014
Preferred stock cash dividend	$ 7			$ 7			$ 21	$ 21
Liquidation preference per share (USD per share)												$ 100,000
Preferred stock, shares outstanding (in shares)	5,000						5,000			5,000
Series G Preferred Stock, Depository Share
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 0.33			$ 0.33			$ 0.99	$ 0.99
Liquidation preference per share (USD per share)												$ 25