Equity Equity (Preferred Stock Classification) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	May 17, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Treasury Stock, Value, Acquired, Cost Method	$ 1,113	$ 999		$ 500	$ 2,100	$ 500
Preferred Stock, Shares Authorized	200,000,000				200,000,000			200,000,000
Preferred Stock, Shares Issued	25,572,200				25,572,200			26,072,200
Preferred Stock, Shares Outstanding	25,572,200				25,572,200			26,072,200
Preferred stock redemption premium	$ 6		$ 0		$ 6	$ 0
Preferred Stock, Redemption Amount							$ 500
Preferred Stock, Par or Stated Value Per Share	$ 0.01				$ 0.01			$ 0.01
Series A Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	27,600,000				27,600,000			27,600,000
Preferred Stock, Shares Issued	24,000,000				24,000,000			24,000,000
Preferred Stock, Shares Outstanding	24,000,000				24,000,000			24,000,000
Series C Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	0				0		500,000	1,500,000
Preferred Stock, Shares Issued	0				0			500,000
Preferred Stock, Shares Outstanding	0				0			500,000
Preferred Stock, Redemption Price Per Share							$ 1,000
Preferred Stock, Dividend Payment Rate, Variable					5.25% Fixed-to-Floating Rate
Preferred stock redemption premium					$ 6
Series D Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	500,000				500,000			500,000
Preferred Stock, Shares Issued	500,000				500,000			500,000
Preferred Stock, Shares Outstanding	500,000				500,000			500,000
Series E Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	32,200				32,200			32,200
Preferred Stock, Shares Issued	32,200				32,200			32,200
Preferred Stock, Shares Outstanding	32,200				32,200			32,200
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	40,000				40,000			40,000
Preferred Stock, Shares Issued	40,000				40,000			40,000
Preferred Stock, Shares Outstanding	40,000				40,000			40,000
Series A Junior Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	10,000,000				10,000,000			10,000,000
Preferred Stock, Shares Issued	0				0			0
Preferred Stock, Shares Outstanding	0				0			0
Not Designated Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	160,827,800				160,827,800			159,327,800
Preferred Stock, Shares Issued	0				0			0
Preferred Stock, Shares Outstanding	0				0			0
Series G Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	1,000,000				1,000,000			1,000,000
Preferred Stock, Shares Issued	1,000,000				1,000,000			1,000,000
Preferred Stock, Shares Outstanding	1,000,000				1,000,000			1,000,000