Loans (Narrative) (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) Score	Dec. 31, 2019 USD ($) Score	Mar. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Loans to Value Percentage	61.00%	63.00%
Loans (see Note 9 for amounts pledged)	$ 38,530,400,000	$ 30,998,900,000	$ 31,247,000,000.0
Average FICO score | Score	752	751
Trial modification, amount	$ 1,500,000	$ 5,500,000
Commitments to lend additional funds to borrowers whose loan terms have been modified in TDRs	$ 18,200,000	$ 23,600,000
Troubled debt restructuring, payment deferral rate (percentage)	49.00%	52.00%
Troubled debt restructuring, covenant relief rate, other (percentage)	51.00%	48.00%
Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (see Note 9 for amounts pledged)	$ 7,833,600,000	$ 5,979,400,000
Loans with terms that permitted negative amortization, unpaid principal balance	0	0
Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (see Note 9 for amounts pledged)	$ 0
Covered Loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (see Note 9 for amounts pledged)		$ 307,800,000