Allowance for Credit Losses - Gross Charge-Offs by Year of Origination (Details) $ in Millions	Mar. 31, 2023 USD ($)
Allowance for Loan and Lease Losses [Roll Forward]
Year one, current fiscal year charge offs	$ 0
Year two, current fiscal year charge offs	5
Year three, current fiscal year charge offs	0
Year four, current fiscal year charge offs	1
Year five, current fiscal year charge offs	2
Prior year charge offs	10
Revolving loans charge offs	4
Total charge offs	22
Commercial: | Commercial, financial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Year one, current fiscal year charge offs	0
Year two, current fiscal year charge offs	5
Year three, current fiscal year charge offs	0
Year four, current fiscal year charge offs	1
Year five, current fiscal year charge offs	0
Prior year charge offs	6
Revolving loans charge offs	2
Total charge offs	14
Commercial: | Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Year one, current fiscal year charge offs	0
Year two, current fiscal year charge offs	0
Year three, current fiscal year charge offs	0
Year four, current fiscal year charge offs	0
Year five, current fiscal year charge offs	2
Prior year charge offs	0
Revolving loans charge offs	0
Total charge offs	2
Consumer: | Consumer Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Year one, current fiscal year charge offs	0
Year two, current fiscal year charge offs	0
Year three, current fiscal year charge offs	0
Year four, current fiscal year charge offs	0
Year five, current fiscal year charge offs	0
Prior year charge offs	1
Revolving loans charge offs	0
Total charge offs	1
Consumer: | Credit Card and Other
Allowance for Loan and Lease Losses [Roll Forward]
Year one, current fiscal year charge offs	0
Year two, current fiscal year charge offs	0
Year three, current fiscal year charge offs	0
Year four, current fiscal year charge offs	0
Year five, current fiscal year charge offs	0
Prior year charge offs	3
Revolving loans charge offs	2
Total charge offs	$ 5