Equity (Preferred Stock - Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2019	Nov. 01, 2018	Jun. 04, 2018	May 22, 2018	Mar. 20, 2018	Nov. 01, 2017
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount						$ 2,000	$ 2,000		$ 1,500		$ 2,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount			$ 985
Preferred Stock, Shares Issued			26,032,200	26,032,200
Preferred stock issued, net of issuance costs			$ 0	$ 1,274	$ 0
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares outstanding			26,032,200	26,032,200
Preferred stock, par value			$ 0.01	$ 0.01
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	5.625%		5.625%
Preferred Stock, Shares Issued			32,200	32,200				32,200
Preferred stock issued, net of issuance costs	$ 780
Payments of Stock Issuance Costs	$ 25
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares outstanding			32,200	32,200
Preferred stock, par value								$ 0.01
Preferred stock, aggregate liquidation preference			$ 25,000					$ 25,000
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Issued			500,000	500,000						500,000
Preferred stock issued, net of issuance costs		$ 494
Payments of Stock Issuance Costs		$ 6
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares outstanding			500,000	500,000
Preferred Stock, Dividend Payment Rate, Variable		5.875% Fixed-to-Floating Rate
Preferred stock, par value										$ 0.01
Preferred stock, aggregate liquidation preference			$ 1,000							$ 1,000
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Issued			1,500,000	1,500,000
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares outstanding			1,500,000	1,500,000
Preferred Stock, Dividend Payment Rate, Variable			5.25% Fixed-to-Floating Rate
Preferred stock, aggregate liquidation preference			$ 1,000
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Issued			24,000,000	24,000,000
Preferred stock redemption price per share			$ 25
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares outstanding			24,000,000	24,000,000
Preferred Stock, Dividend Payment Rate, Variable			Three-month LIBOR + 1.00%, with floor of 4.00%
Fixed Rate1 [Member] | Series D Preferred Stock [Member]
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock, Dividend Payment Rate, Variable			0.05875
Fixed Rate1 [Member] | Series C Preferred Stock [Member]
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock, Dividend Payment Rate, Variable			0.0525
Variable Rate1 [Member] | Series D Preferred Stock [Member]
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock, Dividend Payment Rate, Variable			three-month LIBOR + 2.959%
Variable Rate1 [Member] | Series C Preferred Stock [Member]
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock, Dividend Payment Rate, Variable			three-month LIBOR + 3.575%
RatingAgency [Member] | Series E Preferred Stock [Member]
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, aggregate liquidation preference			$ 25,500
RatingAgency [Member] | Series D Preferred Stock [Member]
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, aggregate liquidation preference			$ 1,020
November2017Authorization [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount			$ 0
May2018Authorization [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount			0
November2018Authorization [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount			0
July2019Authorization [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount			$ 985