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, 2024		Dec. 31, 2023		Mar. 31, 2023	Dec. 31, 2022
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	$ 124		$ 96
Collectively evaluated	2,194		2,226
Total ALLL	2,318	[1]	2,322	[1]	$ 2,215	$ 2,194
Individually evaluated	527		476
Collectively evaluated	115,845		116,642
Total portfolio loans and leases	116,372		117,118
Leveraged leases	244		249
Commercial Leveraged Leases
Financing Receivable, Allowance for Credit Loss [Line Items]
Total ALLL	2		2
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	117		90
Collectively evaluated	1,024		1,040
Total ALLL	1,141		1,130		1,143	1,127
Individually evaluated	322		281
Collectively evaluated	71,594		72,465
Total portfolio loans and leases	71,916		72,746
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	0		0
Collectively evaluated	140		145
Total ALLL	140		145		185	245
Individually evaluated	132		126
Collectively evaluated	16,750		16,784
Total portfolio loans and leases	16,882		16,910
Residential mortgage loans	113		116		128
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	7		6
Collectively evaluated	1,030		1,041
Total ALLL	1,037		1,047		$ 887	$ 822
Individually evaluated	73		69
Collectively evaluated	27,501		27,393
Total portfolio loans and leases	$ 27,574		$ 27,462

[1] Includes $48 and $55 of other short-term investments, $1,420 and $1,573 of portfolio loans and leases, $(26) and $(28) of ALLL, $29 and $10 of other assets, $25 and $14 of other liabilities and $1,274 and $1,409 of long-term debt from consolidated VIEs that are included in their respective captions above at March 31, 2024 and December 31, 2023, respectively. For further information, refer to Note 11.