Allowance for Credit Losses and Credit Quality - Accruing and Non-accrual Loans and Leases (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due
Current		$ 33,690,070	$ 34,185,054
30-89 Days Delinquent and Accruing		268,644	112,676
90 Days or More Delinquent and Accruing		8,256	30,076
Total Accruing		33,966,970	34,327,806
Nonaccrual	$ 73,400	376,721	169,658
Total		34,343,691	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
Nonaccrual			0
Total			246,786
Consumer
Financing Receivable, Recorded Investment, Past Due
Total		10,434,438	11,221,123
Consumer | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		10,191,446	11,028,302
30-89 Days Delinquent and Accruing		117,691	44,105
90 Days or More Delinquent and Accruing		1,347	667
Total Accruing		10,310,484	11,073,074
Nonaccrual		123,954	75,154
Total		10,434,438	11,148,228
Consumer | Portfolios acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due
Total			72,895
Consumer | Residential mortgage
Financing Receivable, Recorded Investment, Past Due
Total		5,790,251	6,179,805
Consumer | Residential mortgage | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		5,700,715	6,056,817
30-89 Days Delinquent and Accruing		22,954	17,245
90 Days or More Delinquent and Accruing		1,347	559
Total Accruing		5,725,016	6,074,621
Nonaccrual		65,235	38,577
Total		5,790,251	6,113,198
Consumer | Home equity
Financing Receivable, Recorded Investment, Past Due
Total		3,302,983	3,498,907
Consumer | Home equity | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		3,160,742	3,434,771
30-89 Days Delinquent and Accruing		90,057	22,568
90 Days or More Delinquent and Accruing		0	0
Total Accruing		3,250,799	3,457,339
Nonaccrual		52,184	35,863
Total		3,302,983	3,493,202
Consumer | Consumer installment
Financing Receivable, Recorded Investment, Past Due
Total		1,341,204	1,542,411
Consumer | Consumer installment | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		1,329,989	1,536,714
30-89 Days Delinquent and Accruing		4,680	4,292
90 Days or More Delinquent and Accruing		0	108
Total Accruing		1,334,669	1,541,114
Nonaccrual		6,535	714
Total		1,341,204	1,541,828
Commercial
Financing Receivable, Recorded Investment, Past Due
Total		23,909,253	23,276,341
Commercial | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		23,498,624	22,939,546
30-89 Days Delinquent and Accruing		150,953	64,728
90 Days or More Delinquent and Accruing		6,909	3,672
Total Accruing		23,656,486	23,007,946
Nonaccrual		252,767	94,504
Total		23,909,253	23,102,450
Commercial | Portfolios acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due
Total			173,891
Commercial | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due
Total		11,557,237	11,439,602
Commercial | Commercial and industrial | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		11,357,324	11,283,832
30-89 Days Delinquent and Accruing		56,320	29,780
90 Days or More Delinquent and Accruing		3,101	331
Total Accruing		11,416,745	11,313,943
Nonaccrual		140,492	53,812
Total		11,557,237	11,367,755
Commercial | Commercial real estate
Financing Receivable, Recorded Investment, Past Due
Total		9,627,330	9,136,870
Commercial | Commercial real estate | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		9,492,853	8,993,360
30-89 Days Delinquent and Accruing		63,981	10,291
90 Days or More Delinquent and Accruing		244	1,440
Total Accruing		9,557,078	9,005,091
Nonaccrual		70,252	29,735
Total		9,627,330	9,034,826
Commercial | Lease financing
Financing Receivable, Recorded Investment, Past Due
Total		2,724,686	2,699,869
Commercial | Lease financing | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		2,648,447	2,662,354
30-89 Days Delinquent and Accruing		30,652	24,657
90 Days or More Delinquent and Accruing		3,564	1,901
Total Accruing		2,682,663	2,688,912
Nonaccrual		42,023	10,957
Total		$ 2,724,686	$ 2,699,869
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Recorded Investment, Past Due
Reclassification of previous purchased credit impaired loans	$ (73,400)