Off balance sheet credit exposure before adoption of credit losses effect of change in method.

No definition available.

Name:	nycb_OffBalanceSheetCreditExposuresBeforeAdoptionOfCreditLossesEffectOfChangeInMethod
Namespace Prefix:	nycb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

+ References

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+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

- Definition

Amount of increase in allowance for credit loss on financing receivable from recovery.

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

- Definition

Amount of writeoff of financing receivable, charged against allowance for credit loss.

+ References

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of credit loss expense (reversal of expense) for financing receivable.

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Balance Type:	debit
Period Type:	duration

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Allowance for Credit Losses on Loans and Leases - Additional Information (Details) - USD ($)		12 Months Ended
	Jan. 01, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans and leases		$ 194,043,000	$ 147,638,000	$ 159,820,000
Increase in allowance for credit losses on loans and leases	$ 1,900,000	3,393,000	1,020,000
Provision for loan losses		62,228,000	7,105,000	$ 18,256,000
Charge-offs		22,178,000	20,307,000
Off-balance sheet credit exposures before adoption of CECL	$ 12,500,000
Unfunded Commitments
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses		11,900,000	$ 461,000
CARES Act
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans and leases		194,000,000.0
Increase in allowance for credit losses on loans and leases		46,400,000
Provision for loan losses		63,300,000
Charge-offs		$ 44,500,000