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		Dec. 31, 2020		Jan. 01, 2020	Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		$ 225			$ 170
Collectively evaluated		2,228			911
Unallocated					121
Total ALLL		2,453	[1]	$ 653	1,202	[1]	$ 1,103	$ 1,196
Individually evaluated		1,863			1,529
Collectively evaluated		106,343			107,295
Purchased credit deteriorated		415			551
Total portfolio loans and leases		108,621			109,375
Leveraged leases		323			429
Portfolio loans and leases	[1],[2]	108,782			109,558
Residential mortgage loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Portfolio loans and leases at fair value		161			183
Commercial Leveraged Leases
Financing Receivable, Allowance for Credit Loss [Line Items]
Total ALLL		3			1
Leveraged leases		323			429
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		114			82
Collectively evaluated		1,342			628
Unallocated					0
Total ALLL		1,456			710		645	753
Individually evaluated		962			413
Collectively evaluated		67,701			69,047
Purchased credit deteriorated		334			498
Total portfolio loans and leases		68,997			69,958
Portfolio loans and leases		68,997			69,958
Residential Mortgage Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		68			55
Collectively evaluated		226			18
Unallocated					0
Total ALLL		294			73		81	89
Individually evaluated		628			814
Collectively evaluated		15,073			15,690
Purchased credit deteriorated		66			37
Total portfolio loans and leases		15,767			16,541
Portfolio loans and leases at fair value		161			183
Residential Mortgage Loans | Residential mortgage loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Portfolio loans and leases		15,767
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		43			33
Collectively evaluated		660			265
Unallocated					0
Total ALLL		703			298		267	234
Individually evaluated		273			302
Collectively evaluated		23,569			22,558
Purchased credit deteriorated		15			16
Total portfolio loans and leases		23,857			22,876
Portfolio loans and leases		39,785			39,600
Consumer | Residential mortgage loans | GNMA loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Portfolio loans and leases		39
Unallocated
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated					0
Collectively evaluated					0
Unallocated					121
Total ALLL		$ 0			121		$ 110	$ 120
Individually evaluated					0
Collectively evaluated					0
Purchased credit deteriorated					0
Total portfolio loans and leases					$ 0

[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.

[2] Includes $161 and $183 of residential mortgage loans measured at fair value at December 31, 2020 and 2019, respectively.