Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Financial assets:
Trading debt securities:	$ 7,100,000	$ 8,400,000
Debt securities available-for-sale, at fair value	3,564,300,000	3,121,000,000.0
Equity securities	8,200,000	8,100,000
Mortgage servicing rights	10,600,000	0
Other assets	1,853,000,000.0	1,091,600,000
Fair value of derivative financial instruments	18,400,000	26,000,000.0
Total	3,971,600,000	3,296,900,000
Financial liabilities:
Fair value of derivative financial instruments	81,600,000	33,800,000
Total	96,200,000	139,000,000.0
Exchange Traded Funds [Member]
Financial assets:
Other assets	47,700,000	35,500,000
Equity Mutual Funds [Member]
Financial assets:
Other assets	3,300,000	20,600,000
Fixed Income Securities [Member]
Financial assets:
Other assets		300,000
Risk Participation Agreements [Member] | Maximum [Member]
Financial liabilities:
Fair Value of risk participation agreements		100,000
US Treasury [Member]
Financial assets:
Trading debt securities:	7,100,000	8,400,000
U.S. Treasury and Agency [Member]
Financial assets:
Debt securities available-for-sale, at fair value	687,100,000	678,000,000.0
GSE Mortgage-Backed Securities [Member]
Financial assets:
Debt securities available-for-sale, at fair value	2,877,200,000	2,443,000,000.0
Interest Rate Swaps [Member]
Financial assets:
Fair value of derivative financial instruments	337,600,000	98,900,000
Financial liabilities:
Fair value of derivative financial instruments	92,100,000	135,000,000.0
Interest Rate Caps [Member]
Financial assets:
Fair value of derivative financial instruments	1,700,000	3,100,000
Financial liabilities:
Fair value of derivative financial instruments	1,700,000	3,100,000
Foreign Exchange Contracts [Member]
Financial assets:
Fair value of derivative financial instruments	1,200,000	900,000
Financial liabilities:
Fair value of derivative financial instruments	1,800,000	800,000
Forward Commitments to Sell Residential Mortgage Loans [Member]
Financial assets:
Fair value of derivative financial instruments	500,000	100,000
Risk Participation Agreements [Member]
Financial liabilities:
Fair value of derivative financial instruments	100,000	0
Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Financial liabilities:
Fair value of derivative financial instruments	500,000	100,000
Level 1 [Member]
Financial assets:
Equity securities	8,200,000	8,100,000
Total	753,400,000	750,600,000
Financial liabilities:
Total	0	0
Level 1 [Member] | Exchange Traded Funds [Member]
Financial assets:
Other assets	47,700,000	35,500,000
Level 1 [Member] | Equity Mutual Funds [Member]
Financial assets:
Other assets	3,300,000	20,600,000
Level 1 [Member] | Fixed Income Securities [Member]
Financial assets:
Other assets		0
Level 1 [Member] | US Treasury [Member]
Financial assets:
Trading debt securities:	7,100,000	8,400,000
Level 1 [Member] | U.S. Treasury and Agency [Member]
Financial assets:
Debt securities available-for-sale, at fair value	687,100,000	678,000,000.0
Level 1 [Member] | GSE Mortgage-Backed Securities [Member]
Financial assets:
Debt securities available-for-sale, at fair value	0	0
Level 1 [Member] | Interest Rate Swaps [Member]
Financial assets:
Fair value of derivative financial instruments	0	0
Financial liabilities:
Fair value of derivative financial instruments	0	0
Level 1 [Member] | Interest Rate Caps [Member]
Financial assets:
Fair value of derivative financial instruments	0	0
Financial liabilities:
Fair value of derivative financial instruments	0	0
Level 1 [Member] | Foreign Exchange Contracts [Member]
Financial assets:
Fair value of derivative financial instruments	0	0
Financial liabilities:
Fair value of derivative financial instruments	0	0
Level 1 [Member] | Forward Commitments to Sell Residential Mortgage Loans [Member]
Financial assets:
Fair value of derivative financial instruments	0	0
Level 1 [Member] | Risk Participation Agreements [Member]
Financial liabilities:
Fair value of derivative financial instruments	0	0
Level 1 [Member] | Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Financial liabilities:
Fair value of derivative financial instruments	0	0
Level 2 [Member]
Financial assets:
Equity securities	0	0
Total	3,218,200,000	2,546,300,000
Financial liabilities:
Total	96,200,000	139,000,000.0
Level 2 [Member] | Exchange Traded Funds [Member]
Financial assets:
Other assets	0	0
Level 2 [Member] | Equity Mutual Funds [Member]
Financial assets:
Other assets	0	0
Level 2 [Member] | Fixed Income Securities [Member]
Financial assets:
Other assets		300,000
Level 2 [Member] | US Treasury [Member]
Financial assets:
Trading debt securities:	0	0
Level 2 [Member] | U.S. Treasury and Agency [Member]
Financial assets:
Debt securities available-for-sale, at fair value	0	0
Level 2 [Member] | GSE Mortgage-Backed Securities [Member]
Financial assets:
Debt securities available-for-sale, at fair value	2,877,200,000	2,443,000,000.0
Level 2 [Member] | Interest Rate Swaps [Member]
Financial assets:
Fair value of derivative financial instruments	337,600,000	98,900,000
Financial liabilities:
Fair value of derivative financial instruments	92,100,000	135,000,000.0
Level 2 [Member] | Interest Rate Caps [Member]
Financial assets:
Fair value of derivative financial instruments	1,700,000	3,100,000
Financial liabilities:
Fair value of derivative financial instruments	1,700,000	3,100,000
Level 2 [Member] | Foreign Exchange Contracts [Member]
Financial assets:
Fair value of derivative financial instruments	1,200,000	900,000
Financial liabilities:
Fair value of derivative financial instruments	1,800,000	800,000
Level 2 [Member] | Forward Commitments to Sell Residential Mortgage Loans [Member]
Financial assets:
Fair value of derivative financial instruments	500,000	100,000
Level 2 [Member] | Risk Participation Agreements [Member]
Financial liabilities:
Fair value of derivative financial instruments	100,000	0
Level 2 [Member] | Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Financial liabilities:
Fair value of derivative financial instruments	500,000	100,000
Level 3 [Member]
Financial assets:
Equity securities	0	0
Total	0	0
Financial liabilities:
Total	0	0
Level 3 [Member] | Exchange Traded Funds [Member]
Financial assets:
Other assets	0	0
Level 3 [Member] | Equity Mutual Funds [Member]
Financial assets:
Other assets	0	0
Level 3 [Member] | Fixed Income Securities [Member]
Financial assets:
Other assets		0
Level 3 [Member] | US Treasury [Member]
Financial assets:
Trading debt securities:	0	0
Level 3 [Member] | U.S. Treasury and Agency [Member]
Financial assets:
Debt securities available-for-sale, at fair value	0	0
Level 3 [Member] | GSE Mortgage-Backed Securities [Member]
Financial assets:
Debt securities available-for-sale, at fair value	0	0
Level 3 [Member] | Interest Rate Swaps [Member]
Financial assets:
Fair value of derivative financial instruments	0	0
Financial liabilities:
Fair value of derivative financial instruments	0	0
Level 3 [Member] | Interest Rate Caps [Member]
Financial assets:
Fair value of derivative financial instruments	0	0
Financial liabilities:
Fair value of derivative financial instruments	0	0
Level 3 [Member] | Foreign Exchange Contracts [Member]
Financial assets:
Fair value of derivative financial instruments	0	0
Financial liabilities:
Fair value of derivative financial instruments	0	0
Level 3 [Member] | Forward Commitments to Sell Residential Mortgage Loans [Member]
Financial assets:
Fair value of derivative financial instruments	0	0
Level 3 [Member] | Risk Participation Agreements [Member]
Financial liabilities:
Fair value of derivative financial instruments	0	0
Level 3 [Member] | Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Financial liabilities:
Fair value of derivative financial instruments	$ 0	$ 0