Loans - Narrative (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) grade		Dec. 31, 2017 USD ($) grade		Mar. 31, 2017 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 27,249,793,000	[1]	$ 27,658,929,000	[1]	$ 19,090,074,000
Allowance - purchased credit-impaired loans	2,555,000		3,200,000		590,000
Provision expense for loan and lease losses	800,000
Financing receivable, modifications, recorded investment	226,000,000		234,400,000
Loans To Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 1,784,553,000		2,099,961,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage	24.00%
Restricted And Secured Consumer Real Estate Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 21,300,000		24,200,000
TRUPS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	306,874,000		306,915,000
Loan loss reserves	$ 25,500,000		25,500,000
Heloc And Real Estate Installment Classes
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR, reduction of interest rate by increment, basis points	0.25%
Modified interest rate increase	2.00%
Permanent Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 379,688,000		399,307,000		409,235,000
Allowance - purchased credit-impaired loans	$ 0				0
TDR, reduction of interest rate by increment, basis points	0.25%
Modified interest rate increase	1.00%
TDRS maturities	40 years
Consumer Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 6,246,552,000		6,367,755,000		4,456,811,000
Concentration risk, percentage	23.00%
Allowance - purchased credit-impaired loans	$ 275,000				$ 350,000
TDRS maturities	30 years
Credit Card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 186,771,000		196,364,000
Credit card workout program, granted rate reduction	0.00%
Allowance For TDRs To Recorded Investment Of TDRs
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan loss reserves	$ 34,700,000		$ 37,300,000
Ratio of the allowance for loan losses to loans	15.00%		16.00%
Loans Held-For-Sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, recorded investment	$ 62,000,000		$ 63,200,000
Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans	20,062,743,000		20,271,968,000
Allowance - purchased credit-impaired loans	$ 2,268,000		2,813,000
Commercial Portfolio Segment | Finance Insurance And Loans To Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of commercial & industrial loan portfolio	29.00%
Commercial Portfolio Segment | Loans To Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans	$ 1,784,553,000		2,099,961,000
Percentage of commercial & industrial loan portfolio	11.00%
Percentage contributed in total loan	7.00%
Commercial Portfolio Segment | Finance And Insurance Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans	$ 2,800,000,000
Percentage of commercial & industrial loan portfolio	18.00%
Percentage contributed in total loan	10.00%
Commercial Portfolio Segment | TRUPS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans	$ 306,874,000		306,915,000
Loan loss reserves	$ 25,500,000		$ 25,500,000
Highest internal grade | grade	13		13
Minimum | Heloc And Real Estate Installment Classes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate	1.00%
Modified interest rate time period	5 years
Minimum | Permanent Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate	2.00%
Modified interest rate time period	5 years
Minimum | Credit Card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment reductions, time period	6 months
Minimum | Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forbearance agreements time period	6 months
Maximum | Heloc And Real Estate Installment Classes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate time period	5 years
Maximum | Permanent Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate time period	5 years
Maximum | Credit Card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment reductions, time period	1 year
Credit card workout program, term extension	5 years
Maximum | Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forbearance agreements time period	12 months
Commercial Loan L G D Grade Twelve | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | grade	12
Commercial Loan L G D Grade One | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | grade	1
Commercial Loan P D Grade Thirteen | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans	$ 500,000
Loan Reassessed | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans	$ 1,000,000
Unlikely to be Collected Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | grade	16
Unlikely to be Collected Financing Receivable | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | grade	16
Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | grade	15
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | grade	14
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | grade	13
Special Mention | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | grade	13
Pass | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | grade	1
Pass | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | grade	12
Commercial Loan P D Grade One
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lowest expected default probability | grade	1

[1] March 31, 2018 and December 31, 2017 include $21.5 million and $22.7 million, respectively, of held-to-maturity consumer mortgage loans secured by residential real estate in process of foreclosure.