Allowance for Credit Losses and Credit Quality - Recorded Investment by Credit Risk Category (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	$ 6,398,663
Loans and leases		$ 34,497,464
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	3,449,977
Loans and leases		23,276,341
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	3,413,759
Loans and leases		11,439,602
Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	0
Loans and leases		9,136,870
Commercial | Lease financing
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	36,218
Loans and leases		2,699,869
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	2,948,686
Loans and leases		11,221,123
Consumer | Residential mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	0
Loans and leases		6,179,805
Consumer | Home equity
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	2,922,199
Loans and leases		3,498,907
Consumer | Consumer installment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	26,487
Loans and leases		1,542,411
Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases		33,603,086
Pass | Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases		22,469,174
Pass | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	3,173,255
Loans and leases		10,930,939
Pass | Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	0
Loans and leases		8,891,361
Pass | Commercial | Lease financing
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	31,963
Loans and leases		2,646,874
Pass | Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases		11,133,912
Pass | Consumer | Residential mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	0
Loans and leases		6,135,096
Pass | Consumer | Home equity
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	2,871,820
Loans and leases		3,457,292
Pass | Consumer | Consumer installment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	26,018
Loans and leases		1,541,524
Special Mention
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases		514,323
Special Mention | Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases		513,302
Special Mention | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	142,520
Loans and leases		315,097
Special Mention | Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	0
Loans and leases		170,114
Special Mention | Commercial | Lease financing
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	3,837
Loans and leases		28,091
Special Mention | Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases		1,021
Special Mention | Consumer | Residential mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	0
Loans and leases		565
Special Mention | Consumer | Home equity
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases		456
Special Mention | Consumer | Consumer installment
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases		0
Substandard
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases		380,055
Substandard | Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases		293,865
Substandard | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	97,984
Loans and leases		193,566
Substandard | Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	0
Loans and leases		75,395
Substandard | Commercial | Lease financing
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	418
Loans and leases		24,904
Substandard | Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases		86,190
Substandard | Consumer | Residential mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	0
Loans and leases		44,144
Substandard | Consumer | Home equity
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	50,379
Loans and leases		41,159
Substandard | Consumer | Consumer installment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Revolving, Converted to Term Loan	469
Loans and leases		$ 887
Equipment Leased to Other Party | Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving Loans and Leases Converted to Term Loans and Leases	$ 226,300