Allowance for Credit Losses - Rollforward of Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 787	$ 715	$ 773
Charge-offs	(49)	(33)	(95)	$ (54)
Recoveries	15	10
Provision for credit losses	55	50	105	100
Ending balance	821	737	821	737	$ 773
Accounting Standards Update [Extensible List]					Accounting Standards Update 2023-02	Accounting Standards Update 2022-02
Loans and leases	62,781		62,781		$ 61,292
Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	887	827	887	827
Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance			773	685	685
Charge-offs			(95)	(54)
Recoveries			21	15
Provision for credit losses	68	45	122	97
Ending balance					773	$ 685
Accounting Standards Update [Extensible List]						Accounting Standards Update 2022-02
Funded commitment | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				(6)	(6)
Ending balance						$ (6)
Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	79	85	83	87	87
Provision for credit losses	(13)	5	(17)	3
Ending balance	66	90	66	90	83	87
Commercial: | Commercial, financial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	348	325
Charge-offs	(24)	(19)	(52)	(33)
Recoveries	12	5
Ending balance	344	326	344	326
Loans and leases	33,452		33,452		32,633
Commercial: | Commercial, financial and industrial | Paycheck Protection Plan
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	19	44	19	44	29
Commercial: | Commercial, financial and industrial | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	388	381	388	381
Commercial: | Commercial, financial and industrial | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance			339	308	308
Charge-offs			(52)	(33)
Recoveries			14	7
Provision for credit losses	8	15	43	43
Ending balance					339	308
Commercial: | Commercial, financial and industrial | Funded commitment | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				1	1
Ending balance						1
Commercial: | Commercial, financial and industrial | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	49	53	49	55	55
Provision for credit losses	(5)	2	(5)	0
Ending balance	44	55	44	55	49	55
Commercial: | Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	181	150
Charge-offs	(19)	(8)	(32)	(10)
Recoveries	0	1
Ending balance	221	159	221	159
Loans and leases	14,669		14,669		14,216
Commercial: | Commercial Real Estate | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	231	183	231	183
Commercial: | Commercial Real Estate | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance			172	146	146
Charge-offs			(32)	(10)
Recoveries			0	1
Provision for credit losses	59	16	81	22
Ending balance					172	146
Commercial: | Commercial Real Estate | Funded commitment | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				0	0
Ending balance						0
Commercial: | Commercial Real Estate | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	18	21	22	22	22
Provision for credit losses	(8)	3	(12)	2
Ending balance	10	24	10	24	22	22
Commercial: | Credit Card and Other
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	190		190		180
Consumer:
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	13,909		13,909		13,650
Consumer: | Consumer Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	231	209
Charge-offs	(1)	(1)	(1)	(1)
Recoveries	2	3
Ending balance	231	221	231	221
Loans and leases	13,909		13,909		13,650
Consumer: | Consumer Real Estate | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	243	232	243	232
Consumer: | Consumer Real Estate | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance			233	200	200
Charge-offs			(1)	(1)
Recoveries			4	5
Provision for credit losses	(1)	10	(5)	24
Ending balance					233	200
Consumer: | Consumer Real Estate | Funded commitment | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				(7)	(7)
Ending balance						(7)
Consumer: | Consumer Real Estate | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	12	11	12	10	10
Provision for credit losses	0	0	0	1
Ending balance	12	11	12	11	12	10
Consumer: | Credit Card and Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	27	31
Charge-offs	(5)	(5)	(10)	(10)
Recoveries	1	1
Ending balance	25	31	25	31
Loans and leases	751		751		793
Consumer: | Credit Card and Other | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	25	31	25	31
Consumer: | Credit Card and Other | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance			29	31	31
Charge-offs			(10)	(10)
Recoveries			3	2
Provision for credit losses	2	4	3	8
Ending balance					29	31
Consumer: | Credit Card and Other | Funded commitment | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				0	0
Ending balance						0
Consumer: | Credit Card and Other | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0	0	0	0
Provision for credit losses	0	0	0	0
Ending balance	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0