Loan Sales and Servicing - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable Including Other Real Estate Owned [Line Items]
Loans held for sale		$ 70,582,000	$ 154,816,000
Transfer of loans to loans held for sale		907,000,000	21,000,000	$ 124,000,000
Recognized charge-off upon transfer of loans to loans held for sale		0	6,500,000	32,500,000
Fair value of MSRs		44,541,000	35,488,000
Originated for sale in secondary market
Accounts, Notes, Loans and Financing Receivable Including Other Real Estate Owned [Line Items]
Residential mortgage loans sold		1,500,000,000	1,100,000,000	1,600,000,000
Recognized net gains on sale of residential mortgage loans		41,900,000	34,700,000	21,500,000
Loans and loans held for sale excluding loans originated for sale in secondary market
Accounts, Notes, Loans and Financing Receivable Including Other Real Estate Owned [Line Items]
Cost of loans and leases sold		466,000,000	108,000,000	204,000,000
Residential mortgage loans sold with retained servicing
Accounts, Notes, Loans and Financing Receivable Including Other Real Estate Owned [Line Items]
Residential mortgage loans sold		1,500,000,000	1,100,000,000	1,500,000,000
Total residential mortgage loans sold, with retained servicing, being serviced		4,400,000,000	3,300,000,000	2,700,000,000
Contractually specified servicing fees, amount		22,100,000	16,000,000	10,500,000
Fair value of MSRs		44,541,000	$ 35,488,000	$ 30,065,000
Mortgage receivable | Residential real estate
Accounts, Notes, Loans and Financing Receivable Including Other Real Estate Owned [Line Items]
Transfer of loans to loans held for sale		396,000,000
Consumer indirect | Consumer loans
Accounts, Notes, Loans and Financing Receivable Including Other Real Estate Owned [Line Items]
Transfer of loans to loans held for sale	$ 511,000,000	$ 511,000,000