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, 2023		Jun. 30, 2023	Dec. 31, 2022		Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	$ 77			$ 122
Collectively evaluated	2,263			2,072
Total ALLL	2,340	[1]	$ 2,327	2,194	[1]	$ 2,099	$ 2,014	$ 1,892
Individually evaluated	441			1,388
Collectively evaluated	119,534			119,969
Total portfolio loans and leases	119,975			121,357
Leveraged leases	248			247
Commercial Leveraged Leases
Financing Receivable, Allowance for Credit Loss [Line Items]
Total ALLL	2			2
Leveraged leases	248			247
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	70			30
Collectively evaluated	1,117			1,097
Total ALLL	1,187		1,199	1,127		1,158	1,165	1,102
Individually evaluated	247			531
Collectively evaluated	74,871			75,858
Total portfolio loans and leases	75,118			76,389
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	1			47
Collectively evaluated	154			198
Total ALLL	155		173	245		254	248	235
Individually evaluated	125			560
Collectively evaluated	17,055			16,945
Total portfolio loans and leases	17,180			17,505
Residential mortgage loans	113			123		125
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	6			45
Collectively evaluated	992			777
Total ALLL	998		$ 955	822		$ 687	$ 601	$ 555
Individually evaluated	69			297
Collectively evaluated	27,608			27,166
Total portfolio loans and leases	$ 27,677			$ 27,463

[1] Includes $59 and $17 of other short-term investments, $1,728 and $185 of portfolio loans and leases, $(27) and $(2) of ALLL, $11 and $2 of other assets, $15 and $9 of other liabilities, and $1,553 and $118 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2023 and December 31, 2022, respectively. For further information, refer to Note 12.