Borrowings - Additional Information (Detail) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Maximum borrowing capacity with FHLB	$ 1,900,000,000
Outstanding short-term letters of credit	435,100,000	$ 535,600,000
Amount of maintained federal fund lines of credit with correspondent banks	504,000,000.0	504,000,000.0
Investment securities collateral for Federal Reserve Bank Discount Window Lending program	85,300,000	94,800,000
Outstanding amount of federal fund line of credit with Federal Reserve Bank of Philadelphia	0	0
Amount of maintained line of credit with correspondent bank - parent company	10,000,000.0	10,000,000.0
Outstanding amount of line of credit with correspondent bank - parent company	0	0
Total committed borrowing capacity	2,000,000,000.0	1,900,000,000
Total committed borrowing capacity available	1,400,000,000	$ 1,200,000,000
Securities Sold under Agreements to Repurchase [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Long-term debt with variable interest rate	$ 10,100,000