Shareholders' Equity - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Feb. 20, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 15, 2019	Apr. 30, 2016	May 31, 2015	Feb. 28, 2014	Aug. 31, 2012
Class of Stock [Line Items]
Preferred stock cash dividend		$ 210	$ 188	$ 182
Series E Preferred Stock
Class of Stock [Line Items]
Redemption price					$ 750
Liquidation preference per share (USD per share)					$ 100,000
Premium from difference between redemption value and net carrying value		$ 22
Premium EPS impact (in USD per share)		$ (0.06)
Preferred stock, shares outstanding (in shares)		7,500	7,500
Preferred dividends declared (USD per share)		$ 6,000	$ 6,000
Preferred stock cash dividend		$ 45	$ 45
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)		$ 1.52	$ 1.52
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)		$ 5,250	$ 5,250
Preferred stock cash dividend		$ 26	$ 26
Series C 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 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)		$ 5,900	$ 5,900
Preferred stock cash dividend		$ 44	$ 44
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 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)		$ 5,250	$ 5,250
Preferred stock cash dividend		$ 40	$ 40
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)		$ 52.50	$ 52.50
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)		$ 5,352	$ 5,352
Preferred stock cash dividend		$ 27	$ 27
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
Subsequent Event | Series C Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 1,313
Preferred stock cash dividend	$ 6
Subsequent Event | Series C Preferred Stock, Depository Share
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 0.33
Subsequent Event | Series D Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 1,475
Preferred stock cash dividend	$ 11
Subsequent Event | Series D Preferred Stock, Depository Share
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 0.37
Subsequent Event | Series F Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 2,625
Preferred stock cash dividend	$ 20
Subsequent Event | Series F Preferred Stock, Depository Share
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 26.25
Subsequent Event | Series G Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 1,338
Preferred stock cash dividend	$ 7
Subsequent Event | Series G Preferred Stock, Depository Share
Class of Stock [Line Items]
Preferred dividends declared (USD per share)	$ 0.33