Stockholders' Equity (Preferred Stock Issued and Outstanding) (Details) - USD ($) $ / shares in Units, $ in Millions				9 Months Ended
	Jun. 01, 2021	Mar. 30, 2021	Mar. 18, 2021	Sep. 30, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Shares issued (in shares)				1,834,000	1,811,000
Shares outstanding (in shares)				1,834,000	1,811,000
Carrying Value				$ 9,954	$ 7,733
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued (in shares)				0	600,000
Shares outstanding (in shares)				0	600,000
Liquidation preference per share (USD per share)				$ 1,000
Carrying Value				$ 0	$ 585
Dividend Rate in Effect	6.00%			0.00%
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued (in shares)				750,000	750,000
Shares outstanding (in shares)				750,000	750,000
Liquidation preference per share (USD per share)				$ 1,000
Carrying Value				$ 728	$ 728
Dividend Rate in Effect				5.95%
Series J Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued (in shares)				600,000	0
Shares outstanding (in shares)				600,000	0
Liquidation preference per share (USD per share)		$ 1,000		$ 1,000
Carrying Value				$ 584	$ 0
Dividend Rate in Effect		4.45%		4.45%
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued (in shares)				400,000	400,000
Shares outstanding (in shares)				400,000	400,000
Liquidation preference per share (USD per share)				$ 1,000
Carrying Value				$ 397	$ 397
Dividend Rate in Effect				7.00%
Series A Preferred Stock [Member] | LIBOR [Member]
Class of Stock [Line Items]
Floating Annual Rate				4.82%
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued (in shares)				6,000	6,000
Shares outstanding (in shares)				6,000	6,000
Liquidation preference per share (USD per share)				$ 100,000
Carrying Value				$ 591	$ 591
Dividend Rate in Effect				4.625%
Series E Preferred Stock [Member] | LIBOR [Member]
Class of Stock [Line Items]
Floating Annual Rate				3.315%
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued (in shares)				5,000	5,000
Shares outstanding (in shares)				5,000	5,000
Liquidation preference per share (USD per share)				$ 100,000
Carrying Value				$ 492	$ 492
Dividend Rate in Effect				5.00%
Series F Preferred Stock [Member] | LIBOR [Member]
Class of Stock [Line Items]
Floating Annual Rate				2.575%
Series G Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued (in shares)				25,000	25,000
Shares outstanding (in shares)				25,000	25,000
Liquidation preference per share (USD per share)				$ 100,000
Carrying Value				$ 2,470	$ 2,470
Dividend Rate in Effect				5.375%
Series G Preferred Stock [Member] | Treasury Rate [Member]
Class of Stock [Line Items]
Dividend term				5 years
Floating Annual Rate				4.971%
Series H Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued (in shares)				25,000	25,000
Shares outstanding (in shares)				25,000	25,000
Liquidation preference per share (USD per share)				$ 100,000
Carrying Value				$ 2,470	$ 2,470
Dividend Rate in Effect				4.00%
Series H Preferred Stock [Member] | Treasury Rate [Member]
Class of Stock [Line Items]
Dividend term				10 years
Floating Annual Rate				3.079%
Series I Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued (in shares)				23,000	0
Shares outstanding (in shares)				23,000	0
Liquidation preference per share (USD per share)			$ 100,000	$ 100,000
Carrying Value				$ 2,222	$ 0
Dividend Rate in Effect			4.00%	4.00%
Dividend term				5 years
Series I Preferred Stock [Member] | Treasury Rate [Member]
Class of Stock [Line Items]
Dividend term				5 years
Floating Annual Rate				3.168%
Maturity period				5 years
Depositary Shares [Member]
Class of Stock [Line Items]
Liquidation preference per share (USD per share)	$ 25	$ 25	$ 1,000
Number of shares issued (in shares)		24,000,000	2,250,000
Ownership interest in shares	2.50%	2.50%	1.00%