Loans and Leases - Summary of Financial Effects of Troubled Debt Restructurings (Details) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($) Investment	Sep. 30, 2019 USD ($) Investment	Sep. 30, 2020 USD ($) Investment	Sep. 30, 2019 USD ($) Investment
Financing Receivable Modifications [Line Items]
Number of loans classified as a non-accrual TDRs \| Investment			43
Pre-Modification Recorded Investment			$ 24,031
Post-Modification Recorded Investment			$ 22,590
Weighted Average Interest Rate, Pre-Modification			5.91%
Weighted Average Interest Rate, Post-Modification			3.08%
Trouble debt restructuring, charge-off amount			$ 1,441
Commercial and Industrial
Financing Receivable Modifications [Line Items]
Number of loans classified as a non-accrual TDRs \| Investment	23	28	42	58
Pre-Modification Recorded Investment	$ 4,508	$ 7,366	$ 8,912	$ 30,910
Post-Modification Recorded Investment	$ 4,508	$ 7,086	$ 7,471	$ 28,179
Weighted Average Interest Rate, Pre-Modification	1.66%	2.99%	2.36%	4.48%
Weighted Average Interest Rate, Post-Modification	1.66%	2.82%	2.20%	4.52%
Trouble debt restructuring, charge-off amount		$ 280	$ 1,441	$ 2,731
Capitalized interest		$ 3		$ 3
Commercial Real Estate
Financing Receivable Modifications [Line Items]
Number of loans classified as a non-accrual TDRs \| Investment			1
Pre-Modification Recorded Investment			$ 15,119
Post-Modification Recorded Investment			$ 15,119
Weighted Average Interest Rate, Pre-Modification			8.00%
Weighted Average Interest Rate, Post-Modification			3.50%

Weighted Average Interest Rate Post Modification

No definition available.

Name:	nycb_WeightedAverageInterestRatePostModification
Namespace Prefix:	nycb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted Average Interest Rate Pre Modification

+ References

No definition available.

+ Details

Name:	nycb_WeightedAverageInterestRatePreModification
Namespace Prefix:	nycb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableModificationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121585226&loc=d3e18845-111554

+ Details

Name:	us-gaap_FinancingReceivablesImpairedTroubledDebtRestructuringWriteDown
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The gross interest income that would have been recorded in the period on troubled debt restructurings, if the loans had been current in accordance with their original terms and had been outstanding throughout the period or since origination, if held for part of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121585226&loc=d3e18794-111554

+ Details

Name:	us-gaap_LoansAndLeasesReceivableImpairedTroubledDebtInterestIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialAndIndustrialSectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: