Allowance for Credit Losses and Credit Quality - Accruing and Non-accrual Loans and Leases (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment, Past Due
Current	$ 35,421,059	$ 33,566,440
30-89 Days Delinquent and Accruing	112,623	215,223
90 Days or More Delinquent  and Accruing	9,436	7,443
Total Accruing	35,543,118	33,789,106
Nonaccrual	677,901	677,302
Total	36,221,019	34,466,408
Consumer
Financing Receivable, Recorded Investment, Past Due
Total	10,526,351	10,524,207
Consumer | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	10,345,329	10,297,888
30-89 Days Delinquent and Accruing	23,556	51,689
90 Days or More Delinquent  and Accruing	1,930	2,028
Total Accruing	10,370,815	10,351,605
Nonaccrual	155,536	172,602
Total	10,526,351	10,524,207
Consumer | Residential mortgage
Financing Receivable, Recorded Investment, Past Due
Total	6,510,981	6,182,045
Consumer | Residential mortgage | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	6,421,403	6,065,379
30-89 Days Delinquent and Accruing	11,171	17,048
90 Days or More Delinquent  and Accruing	1,874	1,965
Total Accruing	6,434,448	6,084,392
Nonaccrual	76,533	97,653
Total	6,510,981	6,182,045
Consumer | Home equity
Financing Receivable, Recorded Investment, Past Due
Total	2,864,142	3,108,736
Consumer | Home equity | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	2,781,347	3,008,450
30-89 Days Delinquent and Accruing	9,798	30,840
90 Days or More Delinquent  and Accruing	56	63
Total Accruing	2,791,201	3,039,353
Nonaccrual	72,941	69,383
Total	2,864,142	3,108,736
Consumer | Consumer installment
Financing Receivable, Recorded Investment, Past Due
Total	1,151,228	1,233,426
Consumer | Consumer installment | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	1,142,579	1,224,059
30-89 Days Delinquent and Accruing	2,587	3,801
90 Days or More Delinquent  and Accruing	0	0
Total Accruing	1,145,166	1,227,860
Nonaccrual	6,062	5,566
Total	1,151,228	1,233,426
Commercial
Financing Receivable, Recorded Investment, Past Due
Total	25,694,668	23,942,201
Commercial | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	25,075,730	23,268,552
30-89 Days Delinquent and Accruing	89,067	163,534
90 Days or More Delinquent  and Accruing	7,506	5,415
Total Accruing	25,172,303	23,437,501
Nonaccrual	522,365	504,700
Total	25,694,668	23,942,201
Commercial | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due
Total	12,856,701	11,422,383
Commercial | Commercial and industrial | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	12,588,529	11,119,453
30-89 Days Delinquent and Accruing	25,413	42,033
90 Days or More Delinquent  and Accruing	2,772	1,458
Total Accruing	12,616,714	11,162,944
Nonaccrual	239,987	259,439
Total	12,856,701	11,422,383
Commercial | Commercial real estate
Financing Receivable, Recorded Investment, Past Due
Total	9,881,341	9,702,587
Commercial | Commercial real estate | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	9,662,431	9,453,743
30-89 Days Delinquent and Accruing	30,490	94,383
90 Days or More Delinquent  and Accruing	0	22
Total Accruing	9,692,921	9,548,148
Nonaccrual	188,420	154,439
Total	9,881,341	9,702,587
Commercial | Lease financing
Financing Receivable, Recorded Investment, Past Due
Total	2,956,626	2,817,231
Commercial | Lease financing | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current	2,824,770	2,695,356
30-89 Days Delinquent and Accruing	33,164	27,118
90 Days or More Delinquent  and Accruing	4,734	3,935
Total Accruing	2,862,668	2,726,409
Nonaccrual	93,958	90,822
Total	$ 2,956,626	$ 2,817,231