Allowance for Credit Losses - Rollforward of Allowance for Credit Losses (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 685,000,000	$ 670,000,000	$ 670,000,000
Charge-offs	0	0
Charge-offs	(22,000,000)	(19,000,000)
Recoveries	6,000,000	9,000,000
Ending balance	715,000,000	622,000,000	685,000,000
Loans and leases	59,045,000,000		$ 58,102,000,000
Accounting Standards Update [Extensible List]			Accounting Standards Update 2022-02
Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	(6,000,000)
Ending balance			$ (6,000,000)
Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	800,000,000	686,000,000
Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	52,000,000	(38,000,000)
Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	87,000,000	66,000,000	66,000,000
Provision for loan and lease losses	(2,000,000)	(2,000,000)
Ending balance	85,000,000	64,000,000	87,000,000
Commercial: | Commercial, financial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	308,000,000	334,000,000	334,000,000
Charge-offs	(14,000,000)	(13,000,000)
Recoveries	3,000,000	3,000,000
Ending balance	325,000,000	287,000,000	308,000,000
Loans and leases	32,172,000,000		31,781,000,000
Commercial: | Commercial, financial and industrial | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,000,000
Ending balance			1,000,000
Commercial: | Commercial, financial and industrial | Paycheck Protection Plan
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	53,000,000	642,000,000	76,000,000
Commercial: | Commercial, financial and industrial | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	378,000,000	330,000,000
Commercial: | Commercial, financial and industrial | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	27,000,000	(37,000,000)
Commercial: | Commercial, financial and industrial | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	55,000,000	46,000,000	46,000,000
Provision for loan and lease losses	(2,000,000)	(3,000,000)
Ending balance	53,000,000	43,000,000	55,000,000
Commercial: | Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	146,000,000	154,000,000	154,000,000
Charge-offs	(2,000,000)	0
Recoveries	0	0
Ending balance	150,000,000	151,000,000	146,000,000
Loans and leases	13,398,000,000		13,228,000,000
Commercial: | Commercial Real Estate | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0
Ending balance			0
Commercial: | Commercial Real Estate | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	171,000,000	163,000,000
Commercial: | Commercial Real Estate | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	6,000,000	(3,000,000)
Commercial: | Commercial Real Estate | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	22,000,000	12,000,000	12,000,000
Provision for loan and lease losses	(1,000,000)	0
Ending balance	21,000,000	12,000,000	22,000,000
Consumer:
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	12,668,000,000		12,253,000,000
Consumer: | Consumer Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	200,000,000	163,000,000	163,000,000
Charge-offs	(1,000,000)	(1,000,000)
Recoveries	2,000,000	5,000,000
Ending balance	209,000,000	164,000,000	200,000,000
Loans and leases	12,668,000,000		12,253,000,000
Consumer: | Consumer Real Estate | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	(7,000,000)
Ending balance			(7,000,000)
Consumer: | Consumer Real Estate | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	220,000,000	173,000,000
Consumer: | Consumer Real Estate | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	15,000,000	(3,000,000)
Consumer: | Consumer Real Estate | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	10,000,000	8,000,000	8,000,000
Provision for loan and lease losses	1,000,000	1,000,000
Ending balance	11,000,000	9,000,000	10,000,000
Consumer: | Credit Card and Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	31,000,000	19,000,000	19,000,000
Charge-offs	(5,000,000)	(5,000,000)
Recoveries	1,000,000	1,000,000
Ending balance	31,000,000	20,000,000	31,000,000
Loans and leases	807,000,000		840,000,000
Consumer: | Credit Card and Other | Accounting Standards Update 2022-02
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0
Ending balance			0
Consumer: | Credit Card and Other | Funded And Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	31,000,000	20,000,000
Consumer: | Credit Card and Other | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan and lease losses	4,000,000	5,000,000
Consumer: | Credit Card and Other | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0	0
Provision for loan and lease losses	0	0
Ending balance	$ 0	$ 0	$ 0