Allowance for Credit Losses and Credit Quality - Recorded Investment by Credit Risk Category (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Allowance for loan and lease losses, other credit loss reserves
Loans and leases	$ 34,466,408	$ 34,497,464
Commercial Loan and Lease Portfolio
Allowance for loan and lease losses, other credit loss reserves
Loans and leases	23,942,201	23,276,341
Commercial Loan and Lease Portfolio | Commercial and industrial
Allowance for loan and lease losses, other credit loss reserves
Loans and leases	11,422,383	11,439,602
Commercial Loan and Lease Portfolio | Commercial real estate
Allowance for loan and lease losses, other credit loss reserves
Loans and leases	9,702,587	9,136,870
Commercial Loan and Lease Portfolio | Lease financing
Allowance for loan and lease losses, other credit loss reserves
Loans and leases	2,817,231	2,699,869
Consumer Loan Portfolio
Allowance for loan and lease losses, other credit loss reserves
Loans and leases	10,524,207	11,221,123
Consumer Loan Portfolio | Residential mortgage
Allowance for loan and lease losses, other credit loss reserves
Loans and leases	6,182,045	6,179,805
Consumer Loan Portfolio | Home equity
Allowance for loan and lease losses, other credit loss reserves
Loans and leases	3,108,736	3,498,907
Consumer Loan Portfolio | Consumer installment
Allowance for loan and lease losses, other credit loss reserves
Loans and leases	$ 1,233,426	1,542,411
Pass
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		33,603,086
Pass | Commercial Loan and Lease Portfolio
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		22,469,174
Pass | Commercial Loan and Lease Portfolio | Commercial and industrial
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		10,930,939
Pass | Commercial Loan and Lease Portfolio | Commercial real estate
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		8,891,361
Pass | Commercial Loan and Lease Portfolio | Lease financing
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		2,646,874
Pass | Consumer Loan Portfolio
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		11,133,912
Pass | Consumer Loan Portfolio | Residential mortgage
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		6,135,096
Pass | Consumer Loan Portfolio | Home equity
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		3,457,292
Pass | Consumer Loan Portfolio | Consumer installment
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		1,541,524
Special mention
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		514,323
Special mention | Commercial Loan and Lease Portfolio
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		513,302
Special mention | Commercial Loan and Lease Portfolio | Commercial and industrial
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		315,097
Special mention | Commercial Loan and Lease Portfolio | Commercial real estate
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		170,114
Special mention | Commercial Loan and Lease Portfolio | Lease financing
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		28,091
Special mention | Consumer Loan Portfolio
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		1,021
Special mention | Consumer Loan Portfolio | Residential mortgage
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		565
Special mention | Consumer Loan Portfolio | Home equity
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		456
Special mention | Consumer Loan Portfolio | Consumer installment
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		0
Substandard
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		380,055
Substandard | Commercial Loan and Lease Portfolio
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		293,865
Substandard | Commercial Loan and Lease Portfolio | Commercial and industrial
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		193,566
Substandard | Commercial Loan and Lease Portfolio | Commercial real estate
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		75,395
Substandard | Commercial Loan and Lease Portfolio | Lease financing
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		24,904
Substandard | Consumer Loan Portfolio
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		86,190
Substandard | Consumer Loan Portfolio | Residential mortgage
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		44,144
Substandard | Consumer Loan Portfolio | Home equity
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		41,159
Substandard | Consumer Loan Portfolio | Consumer installment
Allowance for loan and lease losses, other credit loss reserves
Loans and leases		$ 887