Credit Quality and the Allowance for Loan and Lease Losses - Summary of Transactions in the ALLL by Portfolio Segment (Details) - USD ($) $ in Millions			12 Months Ended
	Jan. 01, 2020		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	$ 1,202	[1]	$ 1,202	[1]	$ 1,103		$ 1,196
Impact of adoption of ASU 2016-13	33
Losses charged-off			(611)		(510)		(450)
Recoveries of losses previously charged-off			140		141		120
Provision for (benefit from) loan and lease losses			1,079		468		237
Balance, end of period	653		2,453	[1]	1,202	[1]	1,103
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Impact of adoption of ASU 2016-13			643
Other Consumer Loans, Point of Sale
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Losses charged-off			(42)		(48)		(29)
Recoveries of losses previously charged-off			42		48		29
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	710		710		645		753
Impact of adoption of ASU 2016-13			31
Losses charged-off			(282)		(127)		(157)
Recoveries of losses previously charged-off			16		19		25
Provision for (benefit from) loan and lease losses			852		173		24
Balance, end of period			1,456		710		645
Commercial | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Impact of adoption of ASU 2016-13			160
Residential Mortgage Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	73		73		81		89
Impact of adoption of ASU 2016-13			2
Losses charged-off			(9)		(9)		(13)
Recoveries of losses previously charged-off			7		5		6
Provision for (benefit from) loan and lease losses			27		(4)		(1)
Balance, end of period			294		73		81
Residential Mortgage Loans | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Impact of adoption of ASU 2016-13			196
Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	298		298		267		234
Impact of adoption of ASU 2016-13			1
Losses charged-off			(320)		(374)		(280)
Recoveries of losses previously charged-off			117		117		89
Provision for (benefit from) loan and lease losses			200		288		224
Balance, end of period			703		298		267
Consumer | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Impact of adoption of ASU 2016-13			408
Unallocated
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	$ 121		121		110		120
Losses charged-off			0		0		0
Recoveries of losses previously charged-off			0		0		0
Provision for (benefit from) loan and lease losses			0		11		(10)
Balance, end of period			0		$ 121		$ 110
Unallocated | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Impact of adoption of ASU 2016-13			$ (121)

[1] Includes $55 and $74 of other short-term investments, $756 and $1,354 of portfolio loans and leases, $(7) and $(7) of ALLL, $5 and $8 of other assets, $2 and $2 of other liabilities and $656 and $1,253 of long-term debt from consolidated VIEs that are included in their respective captions above at December 31, 2020 and 2019, respectively. For further information, refer to Note 13.