Stockholders' Equity (Preferred Stock Issued and Outstanding) (Details) - USD ($) $ / shares in Units, $ in Millions					6 Months Ended
	Jun. 01, 2021	Apr. 06, 2021	Mar. 30, 2021	Mar. 18, 2021	Jun. 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%