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, 2023	Mar. 31, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 715	$ 685	$ 622	$ 685	$ 670	$ 670
Charge-offs	(33)		(21)	(54)	(40)
Recoveries	10		9	15	18
Ending balance	737	$ 715	624	737	624	$ 685
Accounting Standards Update [Extensible List]		Accounting Standards Update 2022-02				Accounting Standards Update 2022-02
Loans and leases	61,295			61,295		$ 58,102
Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		$ (6)		(6)
Ending balance						(6)
Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	827		704	827	704
Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	45		14	97	(24)
Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	85	87	64	87	66	66
Provision for loan and lease losses	5		16	3	14
Ending balance	90	85	80	90	80	87
Commercial: | Commercial, financial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	325	308	287	308	334	334
Charge-offs	(19)		(12)	(33)	(25)
Recoveries	5		1	7	4
Ending balance	326	325	274	326	274	308
Loans and leases	33,116			33,116		31,781
Commercial: | Commercial, financial and industrial | 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 | Paycheck Protection Plan
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	44		375	44	375	76
Commercial: | Commercial, financial and industrial | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	381		327	381	327
Commercial: | Commercial, financial and industrial | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	15		(2)	43	(39)
Commercial: | Commercial, financial and industrial | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	53	55	43	55	46	46
Provision for loan and lease losses	2		10	0	7
Ending balance	55	53	53	55	53	55
Commercial: | Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	150	146	151	146	154	154
Charge-offs	(8)		0	(10)	0
Recoveries	1		1	1	1
Ending balance	159	150	141	159	141	146
Loans and leases	13,891			13,891		13,228
Commercial: | Commercial Real Estate | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		0		0
Ending balance						0
Commercial: | Commercial Real Estate | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	183		158	183	158
Commercial: | Commercial Real Estate | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	16		(11)	22	(14)
Commercial: | Commercial Real Estate | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	21	22	12	22	12	12
Provision for loan and lease losses	3		5	2	5
Ending balance	24	21	17	24	17	22
Consumer:
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	13,475			13,475		12,253
Consumer: | Consumer Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	209	200	164	200	163	163
Charge-offs	(1)		(2)	(1)	(3)
Recoveries	3		6	5	11
Ending balance	221	209	183	221	183	200
Loans and leases	13,475			13,475		12,253
Consumer: | Consumer Real Estate | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		(7)		(7)
Ending balance						(7)
Consumer: | Consumer Real Estate | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	232		193	232	193
Consumer: | Consumer Real Estate | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	10		15	24	12
Consumer: | Consumer Real Estate | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	11	10	9	10	8	8
Provision for loan and lease losses	0		1	1	2
Ending balance	11	11	10	11	10	10
Consumer: | Credit Card and Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	31	31	20	31	19	19
Charge-offs	(5)		(7)	(10)	(12)
Recoveries	1		1	2	2
Ending balance	31	31	26	31	26	31
Loans and leases	813			813		840
Consumer: | Credit Card and Other | 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 | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	31		26	31	26
Consumer: | Credit Card and Other | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	4		12	8	17
Consumer: | Credit Card and Other | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0	0	0	0	0
Provision for loan and lease losses	0		0	0	0
Ending balance	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0