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			9 Months Ended
	Sep. 30, 2021		Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	$ 2,033		$ 2,696	$ 2,453	[1]	$ 1,202
Losses charged-off	(56)		(135)	(268)		(457)
Recoveries of losses previously charged-off	35		34	132		104
Provision (benefit) from loan and lease losses	(58)		(21)	(363)		1,082
Balance, end of period	1,954	[1]	2,574	1,954	[1]	2,574
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	(7)		(9)	(25)		(31)
Recoveries of losses previously charged-off	7		9	25		31
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	1,224		1,502	1,456		710
Losses charged-off	(10)		(66)	(91)		(209)
Recoveries of losses previously charged-off	6		5	40		14
Provision (benefit) from loan and lease losses	(53)		92	(238)		858
Balance, end of period	1,167		1,533	1,167		1,533
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	235		327	294		73
Losses charged-off	(1)		(1)	(3)		(6)
Recoveries of losses previously charged-off	2		2	5		5
Provision (benefit) from loan and lease losses	(1)		(31)	(61)		29
Balance, end of period	235		297	235		297
Initial recognition of ALLL on PCD loans						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	574		867	703		298
Losses charged-off	(45)		(68)	(174)		(242)
Recoveries of losses previously charged-off	27		27	87		85
Provision (benefit) from loan and lease losses	(4)		(82)	(64)		195
Balance, end of period	$ 552		744	$ 552		744
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 $27 and $55 of other short-term investments, $383 and $756 of portfolio loans and leases, $(3) and $(7) of ALLL, $2 and $5 of other assets, $1 and $2 of other liabilities, and $325 and $656 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2021 and December 31, 2020, respectively. For further information, refer to Note 12.