Credit Quality and the Allowance for Loan and Lease Losses - Summary of the ALLL and Related Loans and Leases Classified by Portfolio Segment (Details) - USD ($) $ in Millions		Sep. 30, 2021		Jun. 30, 2021	Dec. 31, 2020		Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		$ 181			$ 225
Collectively evaluated		1,773			2,228
Total ALLL		1,954	[1]	$ 2,033	2,453	[1]	$ 2,574	$ 2,696	$ 1,202
Individually evaluated		1,330			1,863
Collectively evaluated		106,425			106,343
Purchased credit deteriorated					415
Total portfolio loans and leases		107,755			108,621
Leveraged leases		293			323
Total	[1],[2]	107,911			108,782
Residential mortgage loans | GNMA loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Total					39
Commercial Leveraged Leases
Financing Receivable, Allowance for Credit Loss [Line Items]
Total ALLL		2			3
Leveraged leases		293			323
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		89			114
Collectively evaluated		1,078			1,342
Total ALLL		1,167		1,224	1,456		1,533	1,502	710
Individually evaluated		534			962
Collectively evaluated		66,186			67,701
Purchased credit deteriorated					334
Total portfolio loans and leases		66,720			68,997
Total		66,720			68,997
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		50			68
Collectively evaluated		185			226
Total ALLL		235		235	294		297	327	73
Individually evaluated		496			628
Collectively evaluated		15,506			15,073
Purchased credit deteriorated					66
Total portfolio loans and leases		16,002			15,767
Residential mortgage loans		156			161		174
Residential Mortgage | Residential mortgage loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Total		16,002			15,767
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		42			43
Collectively evaluated		510			660
Total ALLL		552		$ 574	703		$ 744	$ 867	$ 298
Individually evaluated		300			273
Collectively evaluated		24,733			23,569
Purchased credit deteriorated					15
Total portfolio loans and leases		25,033			23,857
Total		$ 41,191			39,785
Consumer | Residential mortgage loans | GNMA loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Total					$ 39

[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.

[2] Includes $156 and $161 of residential mortgage loans measured at fair value at September 30, 2021 and December 31, 2020, respectively.