Allowance for Credit Losses and Credit Quality - Accruing and Non-accrual Loans and Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due
Current	$ 33,566,440	$ 34,185,054
30-89 Days Delinquent and Accruing	215,223	112,676
90 Days or More Delinquent  and Accruing	7,443	30,076
Total Accruing	33,789,106	34,327,806
Total nonaccrual	677,302	169,658
Total	34,466,408	34,497,464
Portfolios acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due
Current		217,206
30-89 Days Delinquent and Accruing		3,843
90 Days or More Delinquent  and Accruing		25,737
Total Accruing		246,786
Total nonaccrual		0
Total		246,786
Consumer Loan Portfolio
Financing Receivable, Recorded Investment, Past Due
Total	10,524,207	11,221,123
Consumer Loan Portfolio | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	10,297,888	11,028,302
30-89 Days Delinquent and Accruing	51,689	44,105
90 Days or More Delinquent  and Accruing	2,028	667
Total Accruing	10,351,605	11,073,074
Total nonaccrual	172,602	75,154
Total	10,524,207	11,148,228
Consumer Loan Portfolio | Portfolios acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due
Total		72,895
Consumer Loan Portfolio | Residential mortgage
Financing Receivable, Recorded Investment, Past Due
Total	6,182,045	6,179,805
Consumer Loan Portfolio | Residential mortgage | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	6,065,379	6,056,817
30-89 Days Delinquent and Accruing	17,048	17,245
90 Days or More Delinquent  and Accruing	1,965	559
Total Accruing	6,084,392	6,074,621
Total nonaccrual	97,653	38,577
Total	6,182,045	6,113,198
Consumer Loan Portfolio | Home equity
Financing Receivable, Recorded Investment, Past Due
Total	3,108,736	3,498,907
Consumer Loan Portfolio | Home equity | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	3,008,450	3,434,771
30-89 Days Delinquent and Accruing	30,840	22,568
90 Days or More Delinquent  and Accruing	63	0
Total Accruing	3,039,353	3,457,339
Total nonaccrual	69,383	35,863
Total	3,108,736	3,493,202
Consumer Loan Portfolio | Consumer installment
Financing Receivable, Recorded Investment, Past Due
Total	1,233,426	1,542,411
Consumer Loan Portfolio | Consumer installment | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	1,224,059	1,536,714
30-89 Days Delinquent and Accruing	3,801	4,292
90 Days or More Delinquent  and Accruing	0	108
Total Accruing	1,227,860	1,541,114
Total nonaccrual	5,566	714
Total	1,233,426	1,541,828
Commercial Loan and Lease Portfolio
Financing Receivable, Recorded Investment, Past Due
Total	23,942,201	23,276,341
Commercial Loan and Lease Portfolio | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	23,268,552	22,939,546
30-89 Days Delinquent and Accruing	163,534	64,728
90 Days or More Delinquent  and Accruing	5,415	3,672
Total Accruing	23,437,501	23,007,946
Total nonaccrual	504,700	94,504
Total	23,942,201	23,102,450
Commercial Loan and Lease Portfolio | Portfolios acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due
Total		173,891
Commercial Loan and Lease Portfolio | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due
Total	11,422,383	11,439,602
Commercial Loan and Lease Portfolio | Commercial and industrial | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	11,119,453	11,283,832
30-89 Days Delinquent and Accruing	42,033	29,780
90 Days or More Delinquent  and Accruing	1,458	331
Total Accruing	11,162,944	11,313,943
Total nonaccrual	259,439	53,812
Total	11,422,383	11,367,755
Commercial Loan and Lease Portfolio | Commercial real estate
Financing Receivable, Recorded Investment, Past Due
Total	9,702,587	9,136,870
Commercial Loan and Lease Portfolio | Commercial real estate | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	9,453,743	8,993,360
30-89 Days Delinquent and Accruing	94,383	10,291
90 Days or More Delinquent  and Accruing	22	1,440
Total Accruing	9,548,148	9,005,091
Total nonaccrual	154,439	29,735
Total	9,702,587	9,034,826
Commercial Loan and Lease Portfolio | Lease financing
Financing Receivable, Recorded Investment, Past Due
Total	2,817,231	2,699,869
Commercial Loan and Lease Portfolio | Lease financing | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	2,695,356	2,662,354
30-89 Days Delinquent and Accruing	27,118	24,657
90 Days or More Delinquent  and Accruing	3,935	1,901
Total Accruing	2,726,409	2,688,912
Total nonaccrual	90,822	10,957
Total	$ 2,817,231	$ 2,699,869