Commitments and Credit Risk - Textual (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Other Commitments [Line Items]
Outstanding letters of credit	$ 44,600,000	$ 49,000,000.0
Federal Home Loan Bank Certificates and Obligations (FHLB)
Other Commitments [Line Items]
Outstanding letters of credit	1,200,000,000	1,500,000,000
Standby Letters of Credit
Other Commitments [Line Items]
Deferred revenue	$ 0	0
Minimum
Other Commitments [Line Items]
Term of letter of credit	9 months
Maximum
Other Commitments [Line Items]
Term of letter of credit	15 years
Credit card commitments
Other Commitments [Line Items]
Outstanding commitments	$ 682,700,000	671,500,000
Other loan commitments
Other Commitments [Line Items]
Outstanding commitments	2,400,000,000	2,400,000,000
Fixed Rate Mortgage Loans
Other Commitments [Line Items]
Outstanding commitments	$ 165,900,000	$ 214,000,000.0