Common, Preferred and Treasury Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jul. 30, 2020	Sep. 17, 2019	Aug. 26, 2019	Jun. 05, 2014	Dec. 09, 2013	May 16, 2013	Dec. 31, 2020	Dec. 31, 2019
Preferred stock, Series L
Class of Stock [Line Items]
Issuance of preferred shares (in shares)	350,000
Preferred stock, issued (in shares)	14,000
Preferred stock, dividend rate	4.50%
Issuance of preferred shares	$ 346
Preferred stock, liquidation preference (in usd per share)	$ 25,000
Preferred stock, redemption percentage	100.00%
Preferred stock, Series L | U.S. Treasury Rate
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate (as a percent)	4.215%
Preferred Stock Series K
Class of Stock [Line Items]
Issuance of preferred shares (in shares)		10,000,000
Preferred stock, issued (in shares)		10,000
Preferred stock, dividend rate		4.95%
Issuance of preferred shares		$ 242
Preferred stock, liquidation preference (in usd per share)		$ 25,000
Preferred Stock Class B, Series A
Class of Stock [Line Items]
Issuance of preferred shares (in shares)			200,000
Preferred stock, dividend rate			6.00%
Preferred stock, liquidation preference (in usd per share)			$ 1,000				$ 1,000	$ 1,000
Preferred stock, Series J
Class of Stock [Line Items]
Issuance of preferred shares (in shares)				300,000
Preferred stock, issued (in shares)				12,000
Preferred stock, dividend rate				4.90%
Issuance of preferred shares				$ 297
Preferred stock, liquidation preference (in usd per share)				$ 25,000
Preferred stock, Series J | LIBOR
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate (as a percent)				3.129%
Preferred stock, Series I
Class of Stock [Line Items]
Issuance of preferred shares (in shares)					18,000,000
Preferred stock, issued (in shares)					18,000
Preferred stock, dividend rate					6.625%
Issuance of preferred shares					$ 441
Preferred stock, liquidation preference (in usd per share)					$ 25,000
Preferred stock, Series I | LIBOR
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate (as a percent)					3.71%
Preferred stock, Series H
Class of Stock [Line Items]
Issuance of preferred shares (in shares)						600,000
Preferred stock, issued (in shares)						24,000
Preferred stock, dividend rate						5.10%
Issuance of preferred shares						$ 593
Preferred stock, liquidation preference (in usd per share)						$ 25,000
Preferred stock, Series H | LIBOR
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate (as a percent)						3.033%