Shareholders' Equity - Schedule of Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended				9 Months Ended
	Sep. 30, 2018	Apr. 30, 2016	May 31, 2015	Feb. 28, 2014	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Series D Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary shares issued (shares)				30,000,000
Liquidation preference per share (USD per share)				$ 25
Series D Preferred Stock
Class of Stock [Line Items]
Ownership Interest Per Depositary Share				0.025%
Liquidation preference per share (USD per share)				$ 100,000
Per annum dividend rate					5.90%
Preferred stock					$ 742	$ 742
Series F Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary shares issued (shares)			750,000
Liquidation preference per share (USD per share)			$ 1,000
Series F Preferred Stock
Class of Stock [Line Items]
Ownership Interest Per Depositary Share			1.00%
Liquidation preference per share (USD per share)			$ 100,000
Per annum dividend rate					5.25%
Preferred stock					$ 742	742
Series G Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary shares issued (shares)		20,000,000
Liquidation preference per share (USD per share)		$ 25
Series G Preferred Stock
Class of Stock [Line Items]
Ownership Interest Per Depositary Share		0.025%
Liquidation preference per share (USD per share)		$ 100,000
Per annum dividend rate					5.35%
Preferred stock					$ 493	493
Series H Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary shares issued (shares)	500,000
Liquidation preference per share (USD per share)							$ 1,000
Series H Preferred Stock
Class of Stock [Line Items]
Ownership Interest Per Depositary Share	1.00%
Liquidation preference per share (USD per share)							$ 100,000
Per annum dividend rate					5.625%
Preferred stock					$ 494	$ 494
London Interbank Offered Rate (LIBOR) | Series D Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate, basis spread on variable rate					3.108%
London Interbank Offered Rate (LIBOR) | Series F Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate, basis spread on variable rate					3.597%
London Interbank Offered Rate (LIBOR) | Series G Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate, basis spread on variable rate					3.709%
London Interbank Offered Rate (LIBOR) | Series H Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate, basis spread on variable rate					2.539%