Loans and Leases - Loan Sales (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable
Proceeds from sales of loan	$ 372,354,000	$ 280,640,000	$ 1,044,282,000
Net gains recognized	33,498,000	42,787,000	85,259,000
Consumer real estate
Accounts, Notes, Loans and Financing Receivable
Loans sold during the period	1,000,000,000	1,300,000,000	1,600,000,000
Proceeds from sales of loan	1,100,000,000	1,400,000,000	1,700,000,000
Net gains recognized	33,500,000	37,300,000	50,400,000
Interest-only strips retained on loan sale	4,800,000	3,400,000	16,900,000
Consumer real estate non-accrual loans sold	34,700,000	71,200,000
Servicing assets	0	0
Servicing liability	0	0
Auto finance
Accounts, Notes, Loans and Financing Receivable
Loans sold during the period		424,700,000	2,100,000,000
Proceeds from sales of loan		431,900,000	2,100,000,000
Net gains recognized		5,500,000	34,800,000
Interest-only strips retained on loan sale			5,700,000
Amount of auto finance loans transferred, with servicing retained, to trusts			1,400,000,000
Cash proceeds from securitization			1,500,000,000
Securitization receivable			18,600,000
Net gains on securitization			$ 12,500,000
Servicing assets	0	0
Servicing liability	$ 0	$ 0