Credit Quality and the Allowance for Loan and Lease Losses - Summary of Transactions in the ALLL by Portfolio Segment (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2021		Jun. 30, 2020	Jun. 30, 2021		Jun. 30, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	$ 2,208		$ 2,348	$ 2,453	[1]	$ 1,202
Losses charged-off	(103)		(163)	(211)		(322)
Recoveries of losses previously charged-off	59		33	96		70
Provision (benefit) from loan and lease losses	(131)		478	(305)		1,103
Balance, end of period	2,033	[1]	2,696	2,033	[1]	2,696
Cumulative Effect, Period of Adoption, Adjustment | ASU 2016-13
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period						643
Other Consumer Loans, Point of Sale
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Losses charged-off	(8)		(9)	(18)		(22)
Recoveries of losses previously charged-off	8		9	18		22
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	1,329		1,313	1,456		710
Losses charged-off	(45)		(81)	(81)		(142)
Recoveries of losses previously charged-off	28		3	35		7
Provision (benefit) from loan and lease losses	(88)		267	(186)		767
Balance, end of period	1,224		1,502	1,224		1,502
Initial recognition of ALLL on PCD loans						31
Commercial | Cumulative Effect, Period of Adoption, Adjustment | ASU 2016-13
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period						160
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	247		260	294		73
Losses charged-off	(1)		(2)	(2)		(4)
Recoveries of losses previously charged-off	1		1	3		2
Provision (benefit) from loan and lease losses	(12)		68	(60)		60
Balance, end of period	235		327	235		327
Initial recognition of ALLL on PCD loans			1			2
Residential Mortgage | Cumulative Effect, Period of Adoption, Adjustment | ASU 2016-13
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period						196
Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	632		775	703		298
Losses charged-off	(57)		(80)	(128)		(176)
Recoveries of losses previously charged-off	30		29	58		61
Provision (benefit) from loan and lease losses	(31)		143	(59)		276
Balance, end of period	$ 574		867	$ 574		867
Initial recognition of ALLL on PCD loans						1
Consumer | Cumulative Effect, Period of Adoption, Adjustment | ASU 2016-13
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period						408
Unallocated
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period						121
Losses charged-off						0
Recoveries of losses previously charged-off						0
Provision (benefit) from loan and lease losses						0
Balance, end of period			$ 0			0
Unallocated | Cumulative Effect, Period of Adoption, Adjustment | ASU 2016-13
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period						$ (121)

[1] Includes $33 and $55 of other short-term investments, $455 and $756 of portfolio loans and leases, $(3) and $(7) of ALLL, $3 and $5 of other assets, $1 and $2 of other liabilities, and $400 and $656 of long-term debt from consolidated VIEs that are included in their respective captions above at June 30, 2021 and December 31, 2020, respectively. For further information, refer to Note 11.