Borrowed Funds - Additional Information (Detail)		12 Months Ended
	Nov. 04, 2002 USD ($) shares $ / shares	Dec. 31, 2017 USD ($) Investment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Accrued interest		$ 19,300,000	$ 18,100,000
Short-term FHLB advances		0	$ 300,000,000,000
Short-term FHLB advances weighted average interest rate			0.81%
Short-term FHLB advances, average balance		$ 3,300,000	$ 929,400,000,000	$ 2,300,000,000
Short-term FHLB advances, average balance, weighted average interest rate		0.82%	0.60%	0.42%
Short-term FHLB advances, interest expense		$ 27,000	$ 5,500,000	$ 9,800,000
Interest expense		222,454,000	216,464,000	1,123,360,000
Short-term repurchase agreements		450,000,000	1,500,000,000
Interest expense		452,236,000	387,487,000	1,283,509,000
Federal funds purchased		0	$ 150,000,000
Federal fund purchased Weighted average interest rate			0.75%
Federal funds purchased, average balance		$ 47,900,000	$ 525,400,000	$ 588,800,000
Federal fund purchased Weighted average interest rate		0.87%	0.51%	0.26%
Federal fund purchased, interest expenses		$ 418,000	$ 2,700,000	$ 1,500,000
Junior subordinated debentures		$ 359,179,000	358,879,000
Capital security, call option (in years)	5 years
Dividends on the Capital Securities, deferred period in Years		5 years
Repurchase Agreements
Debt Instrument [Line Items]
Accrued interest		$ 760,000	1,200,000
Interest expense		16,400,000	23,300,000	$ 99,900,000
Short-term repurchase agreements		0	0
Short-term debt, weighted average interest rate				0.31%
Short-term debt, average outstanding amount				$ 197,300,000
Interest expense				614,000
Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Interest expense		186,000,000	172,000,000	230,600,000
Junior Subordinated Debt
Debt Instrument [Line Items]
Interest expense		$ 19,600,000	18,500,000	17,600,000
Number of business trusts owned | Investment		3
New York Community Capital Trust V (BONUSESSM Units) | BONUSESSM units
Debt Instrument [Line Items]
Public offering of Bifurcated Option Note Unit Securities ("BONUSES units") | shares	5,500,000
Public offering of units, offering price per share | $ / shares	$ 50.00
Gross proceeds of BONUSES, debt	$ 275,000,000
Difference between the assigned value and the stated liquidation amount of the capital securities is treated as an original issue discount	92,400,000
Original issue discount amortized amount		$ 66,400,000
New York Community Capital Trust V (BONUSESSM Units) | BONUSESSM units | Warrant
Debt Instrument [Line Items]
Gross proceeds of BONUSES	$ 92,400,000
New York Community Capital Trust V (BONUSESSM Units) | BONUSESSM units | Capital Units
Debt Instrument [Line Items]
Warrant to purchase, number of shares | shares	2.4953
Warrant to purchase, total number of shares | shares	13,700,000
Warrant to purchase, exercise price per share | $ / shares	$ 20.04
Capital security, term (in years)	49 years
Capital security, coupon or distribution rate	6.00%
Capital security, per share liquidation amount | $ / shares	$ 50.00
Gross proceeds of BONUSES	$ 182,600,000
FHLB - NY
Debt Instrument [Line Items]
Unused line of credit		7,100,000,000	7,500,000,000
Borrowings under line of credit		$ 0	$ 10,000,000
Line of credit, weighted-average interest rate			0.78%
Line of credit, average balance			$ 426,500,000	$ 572,700,000
Line of credit, weighted average interest rate			0.59%	0.44%
Interest expense			$ 2,500,000	$ 2,500,000