Other Income and Other Expense - Other Income and Other Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other income:
Credit-related fee income	$ 86,792	$ 82,614	$ 77,580
Other expense:
Professional services	330,900	312,998	289,862
Amortization of capitalized mortgage servicing rights	$ 71,888	49,619	$ 56,172
Wilmington Trust Corporation [Member]
Other expense:
Accrual for Wilmington Trust Corporation legal-related matters		$ 135,000