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, 2025		Dec. 31, 2024		Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	$ 192		$ 117
Collectively evaluated	2,192		2,235
Total ALLL	2,384	[1]	2,352	[1]	$ 2,318	$ 2,322
Individually evaluated	800		622
Collectively evaluated	121,282		119,061
Total portfolio loans and leases	122,082		119,683
Leveraged leases	241		248
Commercial Leveraged Leases
Financing Receivable, Allowance for Credit Loss [Line Items]
Total ALLL	1		1
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	178		106
Collectively evaluated	1,063		1,048
Total ALLL	1,241		1,154		1,141	1,130
Individually evaluated	563		395
Collectively evaluated	74,574		72,898
Total portfolio loans and leases	75,137		73,293
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	1		0
Collectively evaluated	138		146
Total ALLL	139		146		140	145
Individually evaluated	136		131
Collectively evaluated	17,336		17,304
Total portfolio loans and leases	17,472		17,435
Residential mortgage loans	109		108		113
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	13		11
Collectively evaluated	991		1,041
Total ALLL	1,004		1,052		$ 1,037	$ 1,047
Individually evaluated	101		96
Collectively evaluated	29,372		28,859
Total portfolio loans and leases	$ 29,473		$ 28,955

[1] Includes $47 and $51 of other short-term investments, $874 and $1,000 of portfolio loans and leases, $(16) and $(19) of ALLL, $6 and $5 of other assets, $12 and $12 of other liabilities and $774 and $889 of long-term debt from consolidated VIEs that are included in their respective captions above at March 31, 2025 and December 31, 2024, respectively. For further information, refer to Note 7.