Actual Capital Amounts and Ratios for Community Bank in Comparison to Minimum Amounts and Ratios Required (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Common Equity, Tier 1 Amount
Total regulatory capital, Common Equity, Tier 1 Amount	$ 3,869,129	$ 3,748,231
Minimum for capital adequacy purposes, Common Equity, Tier 1 Amount	1,532,448	1,588,699
Excess, Common Equity, Tier 1 Amount	$ 2,336,681	$ 2,159,532
Total regulatory capital, Leverage Capital, Ratio	9.58%	8.00%
Common Equity, Tier 1 Ratio
Total regulatory capital, Common Equity, Tier 1 Ratio	11.36%	10.62%
Minimum for capital adequacy purposes, Common Equity, Tier 1 Ratio	4.50%	4.50%
Excess, Common Equity, Tier 1 Ratio	6.86%	6.12%
Leverage Capital, Amount
Total regulatory capital, Leverage Capital, Amount	$ 4,371,969	$ 3,748,231
Minimum for capital adequacy purposes, Leverage Capital, Amount	1,826,141	1,875,062
Excess, Leverage Capital, Amount	$ 2,545,828	$ 1,873,169
Minimum for capital adequacy purposes, Leverage Capital, Ratio	4.00%	4.00%
Leverage Capital, Ratio
Total regulatory capital, Leverage Capital, Ratio	9.58%	8.00%
Minimum for capital adequacy purposes, Leverage Capital, Ratio	4.00%	4.00%
Excess, Leverage Capital, Ratio	5.58%	4.00%
Excess, Leverage Capital, Ratio	5.58%	4.00%
Risk-Based Capital, Tier 1 Amount
Total regulatory capital, Risk-Based Capital, Tier 1 Amount	$ 4,371,969	$ 3,748,231
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Amount	2,043,265	2,118,266
Excess, Risk-Based Capital, Tier 1 Amount	$ 2,328,704	$ 1,629,965
Risk-Based Capital, Tier 1 Ratio
Total regulatory capital, Risk-Based Capital, Tier 1 Ratio	12.84%	10.62%
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Ratio	6.00%	6.00%
Excess, Risk-Based Capital, Tier 1 Ratio	6.84%	4.62%
Risk-Based Capital, Total Amount
Total regulatory capital, Risk-Based Capital, Total Amount	$ 4,877,208	$ 4,277,759
Minimum for capital adequacy purposes, Risk-Based Capital, Total Amount	2,724,353	2,824,355
Excess, Risk-Based Capital, Total Amount	$ 2,152,855	$ 1,453,404
Risk-Based Capital, Total Ratio
Total regulatory capital, Risk-Based Capital, Total Ratio	14.32%	12.12%
Minimum for capital adequacy purposes, Risk-Based Capital, Total Ratio	8.00%	8.00%
Excess, Risk-Based Capital, Total Ratio	6.32%	4.12%
New York Community Bank
Common Equity, Tier 1 Amount
Total regulatory capital, Common Equity, Tier 1 Amount	$ 4,253,233	$ 3,686,510
Minimum for capital adequacy purposes, Common Equity, Tier 1 Amount	1,424,795	1,477,056
Excess, Common Equity, Tier 1 Amount	$ 2,828,438	$ 2,209,454
Total regulatory capital, Leverage Capital, Ratio	10.06%	8.45%
Common Equity, Tier 1 Ratio
Total regulatory capital, Common Equity, Tier 1 Ratio	13.43%	11.23%
Minimum for capital adequacy purposes, Common Equity, Tier 1 Ratio	4.50%	4.50%
Excess, Common Equity, Tier 1 Ratio	8.93%	6.73%
Leverage Capital, Amount
Total regulatory capital, Leverage Capital, Amount	$ 4,253,233	$ 3,686,510
Minimum for capital adequacy purposes, Leverage Capital, Amount	1,691,041	1,744,601
Excess, Leverage Capital, Amount	$ 2,562,192	$ 1,941,909
Minimum for capital adequacy purposes, Leverage Capital, Ratio	4.00%	4.00%
Leverage Capital, Ratio
Total regulatory capital, Leverage Capital, Ratio	10.06%	8.45%
Minimum for capital adequacy purposes, Leverage Capital, Ratio	4.00%	4.00%
Excess, Leverage Capital, Ratio	6.06%	4.45%
Excess, Leverage Capital, Ratio	6.06%	4.45%
Risk-Based Capital, Tier 1 Amount
Total regulatory capital, Risk-Based Capital, Tier 1 Amount	$ 4,253,233	$ 3,686,510
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Amount	1,899,727	1,969,408
Excess, Risk-Based Capital, Tier 1 Amount	$ 2,353,506	$ 1,717,102
Risk-Based Capital, Tier 1 Ratio
Total regulatory capital, Risk-Based Capital, Tier 1 Ratio	13.43%	11.23%
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Ratio	6.00%	6.00%
Excess, Risk-Based Capital, Tier 1 Ratio	7.43%	5.23%
Risk-Based Capital, Total Amount
Total regulatory capital, Risk-Based Capital, Total Amount	$ 4,387,620	$ 3,843,382
Minimum for capital adequacy purposes, Risk-Based Capital, Total Amount	2,532,969	2,625,877
Excess, Risk-Based Capital, Total Amount	$ 1,854,651	$ 1,217,505
Risk-Based Capital, Total Ratio
Total regulatory capital, Risk-Based Capital, Total Ratio	13.86%	11.71%
Minimum for capital adequacy purposes, Risk-Based Capital, Total Ratio	8.00%	8.00%
Excess, Risk-Based Capital, Total Ratio	5.86%	3.71%