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		Mar. 31, 2021		Dec. 31, 2020		Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		$ 194		$ 225
Collectively evaluated		2,014		2,228
Total ALLL		2,208	[1]	2,453	[1]	$ 2,348	$ 1,202
Individually evaluated		1,669		1,863
Collectively evaluated		107,033		106,343
Purchased credit deteriorated				415
Total portfolio loans and leases		108,702		108,621
Leveraged leases		321		323
Loans	[1],[2]	108,855		108,782
Commercial Leveraged Leases
Financing Receivable, Allowance for Credit Loss [Line Items]
Total ALLL		3		3
Leveraged leases		321		323
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		86		114
Collectively evaluated		1,243		1,342
Total ALLL		1,329		1,456		1,313	710
Individually evaluated		759		962
Collectively evaluated		68,269		67,701
Purchased credit deteriorated				334
Total portfolio loans and leases		69,028		68,997
Loans		69,028		68,997
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		64		68
Collectively evaluated		183		226
Total ALLL		247		294		260	73
Individually evaluated		604		628
Collectively evaluated		15,019		15,073
Purchased credit deteriorated				66
Total portfolio loans and leases		15,623		15,767
Residential mortgage loans		153		161		185
Residential Mortgage | Residential mortgage loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans		15,623		15,767
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		44		43
Collectively evaluated		588		660
Total ALLL		632		703		$ 775	$ 298
Individually evaluated		306		273
Collectively evaluated		23,745		23,569
Purchased credit deteriorated				15
Total portfolio loans and leases		24,051		23,857
Loans		39,827		39,785
Consumer | Residential mortgage loans | GNMA loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans		$ 37		$ 39

[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.

[2] Includes $153 and $161 of residential mortgage loans measured at fair value at March 31, 2021 and December 31, 2020, respectively.