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, 2024		Jun. 30, 2024	Dec. 31, 2023		Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	$ 98			$ 96
Collectively evaluated	2,207			2,226
Total ALLL	2,305	[1]	$ 2,288	2,322	[1]	$ 2,340	$ 2,327	$ 2,194
Individually evaluated	491			476
Collectively evaluated	116,063			116,642
Total portfolio loans and leases	116,554			117,118
Leveraged leases	247			249
Commercial Leveraged Leases
Financing Receivable, Allowance for Credit Loss [Line Items]
Total ALLL	1			2
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	89			90
Collectively evaluated	1,016			1,040
Total ALLL	1,105		1,113	1,130		1,187	1,199	1,127
Individually evaluated	274			281
Collectively evaluated	70,856			72,465
Total portfolio loans and leases	71,130			72,746
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	0			0
Collectively evaluated	143			145
Total ALLL	143		136	145		155	173	245
Individually evaluated	130			126
Collectively evaluated	16,922			16,784
Total portfolio loans and leases	17,052			16,910
Residential mortgage loans	114			116		113
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	9			6
Collectively evaluated	1,048			1,041
Total ALLL	1,057		$ 1,039	1,047		$ 998	$ 955	$ 822
Individually evaluated	87			69
Collectively evaluated	28,285			27,393
Total portfolio loans and leases	$ 28,372			$ 27,462

[1] Includes $50 and $55 of other short-term investments, $1,131 and $1,573 of portfolio loans and leases, $(21) and $(28) of ALLL, $8 and $10 of other assets, $13 and $14 of other liabilities and $1,008 and $1,409 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2024 and December 31, 2023, respectively. For further information, refer to Note 12.