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
	Mar. 31, 2021		Mar. 31, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	$ 2,453	[1]	$ 1,202
Losses charged-off	(109)		(159)
Recoveries of losses previously charged-off	38		37
(Benefit from) provision for loan and lease losses	(174)		625
Balance, end of period	2,208	[1]	2,348
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	(10)		(13)
Recoveries of losses previously charged-off	10		13
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	1,456		710
Losses charged-off	(35)		(61)
Recoveries of losses previously charged-off	7		4
(Benefit from) provision for loan and lease losses	(99)		500
Balance, end of period	1,329		1,313
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	294		73
Losses charged-off	(1)		(2)
Recoveries of losses previously charged-off	1		1
(Benefit from) provision for loan and lease losses	(47)		(8)
Balance, end of period	247		260
Initial recognition of ALLL on PCD loans			1
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	703		298
Losses charged-off	(73)		(96)
Recoveries of losses previously charged-off	30		32
(Benefit from) provision for loan and lease losses	(28)		133
Balance, end of period	$ 632		775
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
(Benefit from) provision for loan and lease losses			0
Balance, end of period			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 $54 and $55 of other short-term investments, $633 and $756 of portfolio loans and leases, $(5) and $(7) of ALLL, $4 and $5 of other assets, $1 and $2 of other liabilities, and $540 and $656 of long-term debt from consolidated VIEs that are included in their respective captions above at March 31, 2021 and December 31, 2020, respectively. For further information, refer to Note 11.