Allowance for Credit Losses and Credit Quality - Accruing and Non-accrual Loans and Leases (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due
Current		$ 35,473,112	$ 34,185,054
30-89 Days Delinquent and Accruing		192,457	112,676
90 Days or More Delinquent and Accruing		5,570	30,076
Total Accruing		35,671,139	34,327,806
Nonaccrual	$ 73,400	250,475	169,658
Total		35,921,614	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		11,398,769	11,221,123
Consumer | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		11,235,252	11,028,302
30-89 Days Delinquent and Accruing		56,428	44,105
90 Days or More Delinquent and Accruing		973	667
Total Accruing		11,292,653	11,073,074
Nonaccrual		106,116	75,154
Total		11,398,769	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		6,435,314	6,179,805
Consumer | Residential mortgage | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		6,350,832	6,056,817
30-89 Days Delinquent and Accruing		21,949	17,245
90 Days or More Delinquent and Accruing		553	559
Total Accruing		6,373,334	6,074,621
Nonaccrual		61,980	38,577
Total		6,435,314	6,113,198
Consumer | Consumer installment
Financing Receivable, Recorded Investment, Past Due
Total		1,509,953	1,542,411
Consumer | Consumer installment | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		1,504,344	1,536,714
30-89 Days Delinquent and Accruing		4,615	4,292
90 Days or More Delinquent and Accruing		5	108
Total Accruing		1,508,964	1,541,114
Nonaccrual		989	714
Total		1,509,953	1,541,828
Consumer | Home equity
Financing Receivable, Recorded Investment, Past Due
Total		3,453,502	3,498,907
Consumer | Home equity | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		3,380,076	3,434,771
30-89 Days Delinquent and Accruing		29,864	22,568
90 Days or More Delinquent and Accruing		415	0
Total Accruing		3,410,355	3,457,339
Nonaccrual		43,147	35,863
Total		3,453,502	3,493,202
Commercial
Financing Receivable, Recorded Investment, Past Due
Total		24,522,845	23,276,341
Commercial | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		24,237,860	22,939,546
30-89 Days Delinquent and Accruing		136,029	64,728
90 Days or More Delinquent and Accruing		4,597	3,672
Total Accruing		24,378,486	23,007,946
Nonaccrual		144,359	94,504
Total		24,522,845	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		12,326,943	11,439,602
Commercial | Commercial and industrial | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		12,188,493	11,283,832
30-89 Days Delinquent and Accruing		54,183	29,780
90 Days or More Delinquent and Accruing		110	331
Total Accruing		12,242,786	11,313,943
Nonaccrual		84,157	53,812
Total		12,326,943	11,367,755
Commercial | Commercial real estate
Financing Receivable, Recorded Investment, Past Due
Total		9,486,904	9,136,870
Commercial | Commercial real estate | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		9,395,692	8,993,360
30-89 Days Delinquent and Accruing		42,738	10,291
90 Days or More Delinquent and Accruing		1,442	1,440
Total Accruing		9,439,872	9,005,091
Nonaccrual		47,032	29,735
Total		9,486,904	9,034,826
Commercial | Lease financing
Financing Receivable, Recorded Investment, Past Due
Total		2,708,998	2,699,869
Commercial | Lease financing | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		2,653,675	2,662,354
30-89 Days Delinquent and Accruing		39,108	24,657
90 Days or More Delinquent and Accruing		3,045	1,901
Total Accruing		2,695,828	2,688,912
Nonaccrual		13,170	10,957
Total		$ 2,708,998	$ 2,699,869
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	73,400
Reclassification of previous purchased credit impaired loans	$ 73,400