Allowance for Credit Losses and Credit Quality - Accruing and Non-accrual Loans and Leases (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due
Current		$ 35,051,381	$ 34,185,054
30-89 Days Delinquent and Accruing		184,976	112,676
90 Days or More Delinquent and Accruing		8,016	30,076
Total Accruing		35,244,373	34,327,806
Nonaccrual	$ 73,400	291,451	169,658
Total		35,535,824	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		10,999,357	11,221,123
Consumer | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		10,848,937	11,028,302
30-89 Days Delinquent and Accruing		32,681	44,105
90 Days or More Delinquent and Accruing		749	667
Total Accruing		10,882,367	11,073,074
Nonaccrual		116,990	75,154
Total		10,999,357	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		6,123,118	6,179,805
Consumer | Residential mortgage | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		6,037,390	6,056,817
30-89 Days Delinquent and Accruing		17,217	17,245
90 Days or More Delinquent and Accruing		749	559
Total Accruing		6,055,356	6,074,621
Nonaccrual		67,762	38,577
Total		6,123,118	6,113,198
Consumer | Consumer installment
Financing Receivable, Recorded Investment, Past Due
Total		1,430,655	1,542,411
Consumer | Consumer installment | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		1,426,008	1,536,714
30-89 Days Delinquent and Accruing		2,979	4,292
90 Days or More Delinquent and Accruing		0	108
Total Accruing		1,428,987	1,541,114
Nonaccrual		1,668	714
Total		1,430,655	1,541,828
Consumer | Home equity
Financing Receivable, Recorded Investment, Past Due
Total		3,445,584	3,498,907
Consumer | Home equity | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		3,385,539	3,434,771
30-89 Days Delinquent and Accruing		12,485	22,568
90 Days or More Delinquent and Accruing		0	0
Total Accruing		3,398,024	3,457,339
Nonaccrual		47,560	35,863
Total		3,445,584	3,493,202
Commercial
Financing Receivable, Recorded Investment, Past Due
Total		24,536,467	23,276,341
Commercial | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		24,202,444	22,939,546
30-89 Days Delinquent and Accruing		152,295	64,728
90 Days or More Delinquent and Accruing		7,267	3,672
Total Accruing		24,362,006	23,007,946
Nonaccrual		174,461	94,504
Total		24,536,467	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		12,200,721	11,439,602
Commercial | Commercial and industrial | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		12,043,000	11,283,832
30-89 Days Delinquent and Accruing		57,542	29,780
90 Days or More Delinquent and Accruing		1,995	331
Total Accruing		12,102,537	11,313,943
Nonaccrual		98,184	53,812
Total		12,200,721	11,367,755
Commercial | Commercial real estate
Financing Receivable, Recorded Investment, Past Due
Total		9,628,344	9,136,870
Commercial | Commercial real estate | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		9,517,890	8,993,360
30-89 Days Delinquent and Accruing		52,560	10,291
90 Days or More Delinquent and Accruing		373	1,440
Total Accruing		9,570,823	9,005,091
Nonaccrual		57,521	29,735
Total		9,628,344	9,034,826
Commercial | Lease financing
Financing Receivable, Recorded Investment, Past Due
Total		2,707,402	2,699,869
Commercial | Lease financing | Financial Asset Originated
Financing Receivable, Recorded Investment, Past Due
Current		2,641,554	2,662,354
30-89 Days Delinquent and Accruing		42,193	24,657
90 Days or More Delinquent and Accruing		4,899	1,901
Total Accruing		2,688,646	2,688,912
Nonaccrual		18,756	10,957
Total		$ 2,707,402	$ 2,699,869
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Recorded Investment, Past Due
Reclassification of previous purchased credit impaired loans	$ (73,400)