Loans - Narrative (Details) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2020		Dec. 31, 2019		Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 32,708,937,000	[1]	$ 31,061,111,000	[1]		$ 29,712,810,000
Troubled debt restructurings loans	192,600,000		206,300,000
Allowance for loan losses	$ 537,881,000		200,307,000		$ 444,490,000	192,749,000	$ 184,911,000	$ 180,424,000
Loans to Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans collateralized with government guaranteed loans	95.00%
Allowance For TDRs To Recorded Investment Of TDRs
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 13,600,000		$ 19,700,000
Ratio of the allowance for loan losses to loans	7.00%		10.00%
Loans Held For Sale, Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings loans	$ 45,100,000		$ 51,100,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses			158,598,000
Allowance - purchased credit-impaired loans			848,000
Commercial | Loans to Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, before allowance for credit loss	$ 4,000,000,000.0
Percentage of commercial & industrial loan portfolio	19.00%
Percentage contributed in total loan	12.00%
Commercial | Finance Insurance And Loans To Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of commercial & industrial loan portfolio	31.00%
Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 21,393,893,000		20,051,091,000			19,054,269,000
Allowance for loan losses	318,722,000		122,486,000		254,516,000	116,096,000	103,713,000	98,947,000
Commercial | Finance And Insurance Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, before allowance for credit loss	$ 2,500,000,000
Percentage of commercial & industrial loan portfolio	12.00%
Percentage contributed in total loan	8.00%
Consumer | Consumer Real Estate (a)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 6,052,393,000		6,177,139,000			6,303,134,000
Modified interest rate increase	1.00%
TDRS Maturities	40 years
Allowance for loan losses	$ 143,757,000		28,443,000		123,022,000	31,532,000	34,154,000	37,439,000
Consumer | Credit Card and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	449,310,000		495,864,000			494,376,000
Allowance for loan losses	$ 18,117,000		13,266,000		$ 19,327,000	12,168,000	$ 12,662,000	$ 12,727,000
Consumer | Permanent Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR, reduction of interest rate by increment, basis points	0.25%
Consumer | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage	19.00%
Minimum | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forbearance agreements time period	6 months
Minimum | Consumer | Consumer Real Estate (a)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate	2.00%
Modified interest rate time period	5 years
Maximum | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forbearance agreements time period	12 months
Maximum | Consumer | Consumer Real Estate (a)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate time period	5 years
TRUPS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Small bank and business loan, total asset maximum cap	$ 15,000,000,000
TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	209,177,000		218,287,000
Allowance for loan losses	$ 18,400,000		19,100,000
Heloc And Real Estate Installment Classes | Consumer | Consumer Real Estate (a)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate increase	2.00%
TDR, reduction of interest rate by increment, basis points	0.25%
Heloc And Real Estate Installment Classes | Minimum | Consumer | Consumer Real Estate (a)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate	1.00%
Modified interest rate time period	5 years
Heloc And Real Estate Installment Classes | Maximum | Consumer | Consumer Real Estate (a)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate time period	5 years
Credit Card | Consumer | Credit Card and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 167,344,000		201,171,000
Credit card workout program, granted rate reduction	0.00%
Credit Card | Minimum | Consumer | Credit Card and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment reductions, time period	6 months
Credit Card | Maximum | Consumer | Credit Card and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment reductions, time period	1 year
Credit card workout program, term extension	5 years
Purchased credit-impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income						68,799,000
Allowance for loan losses						1,989,000
Allowance - purchased credit-impaired loans			2,000,000.0
Allowance for loan and lease losses write-offs, net			5,800,000
Provision for loan, lease, and other losses			1,300,000
Purchased credit-impaired loans | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income						33,840,000
Allowance for loan losses						854,000
Purchased credit-impaired loans | Consumer | Consumer Real Estate (a)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income						26,829,000
Allowance for loan losses						1,078,000
Purchased credit-impaired loans | Consumer | Credit Card and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income						903,000
Allowance for loan losses						$ 57,000
PD Grade 1 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lowest expected default probability	1
Allowance for loan losses			69,000
PD Grade 1 | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 2,674,017,000
Loss | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	16
Loss | Maximum | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	16
Pass | Minimum | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	1
Pass | Maximum | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	12
Special Mention | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	13
Special Mention | Minimum | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	13
Substandard | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	14
Doubtful | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	15
Loan Reassessed | Minimum | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 1,000,000
PD Grade 13 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses			$ 8,142,000
PD Grade 13 | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	336,048,000
PD Grade 13 | Minimum | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 500,000
LGD Grade 1 | Minimum | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	1
LGD Grade 12 | Maximum | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	12
Paycheck Protection Plan | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 2,100,000,000

[1] June 30, 2020 and December 31, 2019 include $16.9 million and $18.8 million, respectively, of held-to-maturity consumer mortgage loans secured by residential real estate in process of foreclosure.