Securities - Additional Information (Detail)		1 Months Ended		12 Months Ended
	Jan. 01, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) Security Securities	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Investment [Line Items]
Debt security available for sale with fair values pledged with collateral for public deposits		$ 2,200,000,000		$ 2,430,000,000	$ 2,200,000,000
Debt security available for sale with a held-to-maturity pledged with collateral for public deposits		1,490,000,000		$ 1,470,000,000	1,490,000,000
Percentage of securities available for sale				8.00%
Number of debt securities owned | Security				2,242
Number of debt securities classified as available-for-sale | Security				101
Number of debt securities classified as held-to-maturity | Securities				79
Available-for-sale unrealized losses		(69,300,000)		$ (6,900,000)	(69,300,000)
Held-to-maturity unrealized losses		(52,300,000)		(700,000)	(52,300,000)
Impairment of investments				0	0	$ 0
Loss on sales of Securities				400,000	10,000,000.0	27,500,000
Net security losses				200,000	(9,800,000)	(25,400,000)
Available-for-sale securities, amortized cost			$ 9,600,000			9,600,000
Equity securities, at fair value			8,700,000			8,700,000
Unrealized gain on equity securities				1,500,000	600,000
Impairment of investments				0
Dividend income on capital stock				$ 186,500,000	184,200,000	153,700,000
Federal Reserve Bank stock percentage				6.00%
Accounting Standards Update 2016-01 [Member]
Investment [Line Items]
Cumulative-effect transition adjustment to retained earnings	$ (600,000)
Investment in Federal Home Loan Bank Stock [Member]
Investment [Line Items]
Impairment of investments				$ 0
Dividend income on capital stock				7,000,000.0	8,300,000	6,600,000
FHLB of New York [Member]
Investment [Line Items]
Acquired shares of capital stock		700,000		700,000	700,000
Dividend income on capital stock				3,800,000	5,100,000	3,700,000
Acquired shares of capital stock		178,500,000		203,800,000	178,500,000
FHLB of Boston [Member]
Investment [Line Items]
Acquired shares of capital stock		124,200,000		136,600,000	124,200,000
GSE Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for-sale unrealized losses		(48,200,000)		(4,100,000)	(48,200,000)
Held-to-maturity unrealized losses		(33,200,000)		$ (300,000)	(33,200,000)
Available for sale securities average maturity period				18 years
Amortized cost of securities, sold		235,500,000
Loss on sales of Securities		10,000,000.0
State and Municipal [Member]
Investment [Line Items]
Held-to-maturity unrealized losses		$ (18,400,000)		$ (400,000)	(18,400,000)
Available for sale securities average maturity period				9 years
U.S. Treasury and CMO Securities [Member]
Investment [Line Items]
Amortized cost of securities, sold			291,300,000			486,900,000
Loss on sales of Securities			$ 10,000,000.0			15,700,000
Net security losses				$ 200,000	$ (9,800,000)	$ (25,400,000)