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, 2025		Jun. 30, 2025	Dec. 31, 2024		Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	$ 170			$ 117
Collectively evaluated	2,095			2,235
Total ALLL	2,265	[1]	$ 2,412	2,352	[1]	$ 2,305	$ 2,288	$ 2,322
Individually evaluated	622			622
Collectively evaluated	122,401			119,061
Total portfolio loans and leases	123,023			119,683
Leveraged leases	242			248
Commercial Leveraged Leases
Financing Receivable, Allowance for Credit Loss [Line Items]
Total ALLL	2			1
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	156			106
Collectively evaluated	1,026			1,048
Total ALLL	1,182		1,293	1,154		1,105	1,113	1,130
Individually evaluated	380			395
Collectively evaluated	74,043			72,898
Total portfolio loans and leases	74,423			73,293
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	0			0
Collectively evaluated	133			146
Total ALLL	133		134	146		143	136	145
Individually evaluated	137			131
Collectively evaluated	17,400			17,304
Total portfolio loans and leases	17,537			17,435
Residential mortgage loans	107			108		114
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	14			11
Collectively evaluated	936			1,041
Total ALLL	950		$ 985	1,052		$ 1,057	$ 1,039	$ 1,047
Individually evaluated	105			96
Collectively evaluated	30,958			28,859
Total portfolio loans and leases	$ 31,063			$ 28,955

[1] Includes $42 and $51 of other short-term investments, $649 and $1,000 of portfolio loans and leases, $(11) and $(19) of ALLL, $4 and $5 of other assets, $11 and $12 of other liabilities and $563 and $889 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2025 and December 31, 2024, respectively. For further information, refer to Note 7.