Equity (Preferred Stock - Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 01, 2018	May 01, 2018	Nov. 01, 2017	Nov. 10, 2016
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount				$ 2,000	$ 1,500	$ 2,000	$ 3,000
Preferred Stock, Shares Issued	26,032,200	25,500,000
Preferred stock issued, net of issuance costs	$ 1,274	$ 0	$ 0
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares outstanding	26,032,200	25,500,000
Preferred stock, par value $0.01 per share; $3,405 and $2,100 aggregate liquidation preference, respectively	$ 0.01	$ 0.01
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	5.625%
Preferred Stock, Shares Issued	32,200	0
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	0
Preferred stock, par value $0.01 per share; $3,405 and $2,100 aggregate liquidation preference, respectively	$ 0.01
Preferred stock, aggregate liquidation preference	$ 25,000
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Issued	500,000	0
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	0
Preferred Stock, Dividend Payment Rate, Variable	5.875% Fixed-to-Floating Rate
Preferred stock, par value $0.01 per share; $3,405 and $2,100 aggregate liquidation preference, respectively	$ 0.01
Preferred stock, aggregate liquidation preference	$ 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