Equity (Preferred Stock - Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended		3 Months Ended				12 Months Ended
	Sep. 10, 2020	Jan. 15, 2020	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 11, 2020	Jul. 31, 2019	Nov. 01, 2018	Jun. 04, 2018	May 22, 2018	Mar. 20, 2018
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount												$ 3,000	$ 2,000	$ 2,000		$ 1,500
Stock Repurchase Program, Remaining Authorized Repurchase Amount					$ 2,800				$ 2,800
Preferred Stock, Shares Issued					26,072,200				26,072,200	26,032,200
Preferred stock issued, net of issuance costs									$ 1,961	$ 0	$ 1,274
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares outstanding					26,072,200				26,072,200	26,032,200
Preferred stock, par value					$ 0.01				$ 0.01	$ 0.01
Preferred Stock, Shares Authorized					200,000,000				200,000,000	200,000,000
Preferred stock redemption premium					$ 0	$ 14	$ 0	$ 0	$ 14	$ 0	$ 0
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage			5.625%						562.50%
Preferred Stock, Shares Issued					32,200				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	32,200
Preferred stock, par value															$ 0.01
Preferred stock, aggregate liquidation preference					$ 25,000				$ 25,000						$ 25,000
Preferred Stock, Shares Authorized					32,200				32,200	32,200
Series E Preferred Stock [Member] | Depositary Share [Member]
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, aggregate liquidation preference					$ 25				$ 25
Fixed-to-Floating Rate Non-Cumulative Preferred Stock, Series D, par value $0.01
Class of Stock [Line Items]
Preferred Stock, Shares Issued					500,000				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	500,000
Preferred Stock, Dividend Payment Rate, Variable				5.875
Preferred stock, par value																	$ 0.01
Preferred stock, aggregate liquidation preference					$ 1,000				$ 1,000								$ 1,000
Preferred Stock, Shares Authorized					500,000				500,000	500,000
Fixed-to-Floating Rate Non-Cumulative Preferred Stock, Series C, par value $0.01
Class of Stock [Line Items]
Preferred Stock, Shares Issued					500,000				500,000	1,500,000
Preferred stock redemption price per share					$ 1,000				$ 1,000
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares outstanding					500,000				500,000	1,500,000
Preferred Stock, Dividend Payment Rate, Variable									5.25% Fixed-to-Floating Rate
Preferred stock, aggregate liquidation preference					$ 1,000				$ 1,000
Preferred Stock, Shares Authorized					1,500,000				1,500,000	1,500,000
Redeem and Canceled Preferred Stock [Line Items]					1,000,000				1,000,000
Preferred stock redemption premium									$ 14
Preferred Stock, Redemption Amount					$ 1,000				$ 1,000
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Issued					24,000,000				24,000,000	24,000,000
Preferred stock redemption price per share					$ 25				$ 25
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares outstanding					24,000,000				24,000,000	24,000,000
Preferred Stock, Dividend Payment Rate, Variable									Three-month LIBOR + 1.00%, with floor of 4.00%
Preferred Stock, Shares Authorized					27,600,000				27,600,000	27,600,000
Depositary Shares, each representing a 1/1,000th interest in a share of 4.75% Non-Cumulative Preferred Stock, Series F
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage		4.75%							475.00%
Preferred Stock, Shares Issued		40,000			40,000				40,000	0
Preferred stock issued, net of issuance costs		$ 972
Payments of Stock Issuance Costs		$ 28
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares outstanding					40,000				40,000	0
Preferred stock, par value		$ 0.01
Preferred stock, aggregate liquidation preference		$ 25,000			$ 25,000				$ 25,000
Preferred Stock, Shares Authorized					40,000				40,000	0
Depositary Shares, each representing a 1/1,000th interest in a share of 4.75% Non-Cumulative Preferred Stock, Series F | Depositary Share [Member]
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, aggregate liquidation preference					$ 25				$ 25
Fixed Rate Reset Non-Cumulative Preferred Stock, Series G, par value $0.01
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	3.85%								385.00%
Preferred Stock, Shares Issued	1,000,000				1,000,000				1,000,000	0
Preferred stock issued, net of issuance costs	$ 989
Payments of Stock Issuance Costs	$ 11
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares outstanding					1,000,000				1,000,000	0
Preferred stock, par value	$ 0.01
Preferred stock, aggregate liquidation preference	$ 1,000				$ 1,000				$ 1,000
Preferred Stock, Shares Authorized					1,000,000				1,000,000	0
Treasury Shares Issued For Stock Options [Member]
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Stock Issued During Period, Shares, Treasury Stock Reissued									0	0	0
Fixed Rate1 [Member] | Fixed-to-Floating Rate Non-Cumulative Preferred Stock, Series D, par value $0.01
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock, Dividend Payment Rate, Variable									5.875%
Fixed Rate1 [Member] | Fixed-to-Floating Rate Non-Cumulative Preferred Stock, Series C, par value $0.01
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock, Dividend Payment Rate, Variable									5.250%
Variable Rate1 [Member] | Fixed-to-Floating Rate Non-Cumulative Preferred Stock, Series D, par value $0.01
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] | Fixed-to-Floating Rate Non-Cumulative Preferred Stock, Series C, par value $0.01
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock, Dividend Payment Rate, Variable									three-month LIBOR + 3.575%
Variable Rate1 [Member] | Fixed Rate Reset Non-Cumulative Preferred Stock, Series G, par value $0.01
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock, Dividend Payment Rate, Variable									five year treasury rate, reset every five years, + 3.576%
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				$ 25,500
RatingAgency [Member] | Series E Preferred Stock [Member] | Depositary Share [Member]
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, aggregate liquidation preference					25.50				25.50
RatingAgency [Member] | Fixed-to-Floating Rate Non-Cumulative Preferred Stock, Series D, par value $0.01
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, aggregate liquidation preference					1,020				1,020
RatingAgency [Member] | Depositary Shares, each representing a 1/1,000th interest in a share of 4.75% Non-Cumulative Preferred Stock, Series F
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, aggregate liquidation preference					25,500				25,500
RatingAgency [Member] | Depositary Shares, each representing a 1/1,000th interest in a share of 4.75% Non-Cumulative Preferred Stock, Series F | Depositary Share [Member]
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, aggregate liquidation preference					25.50				25.50
RatingAgency [Member] | Fixed Rate Reset Non-Cumulative Preferred Stock, Series G, par value $0.01
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, aggregate liquidation preference					$ 1,020				$ 1,020
May2018Authorization [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount					$ 0				$ 0
November2018Authorization [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount					0				0
July2019Authorization [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount					0				0
December2020Authorization
Class of Stock [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount					$ 2,835				$ 2,835