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Allowance for Loan and Lease Losses - Additional Information (Details) - USD ($) | Sep. 30, 2020 | Dec. 31, 2019
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Receivables [Abstract] |  |
Off-balance sheet credit exposures | $ 12,300,000 | $ 461,000
Off-balance sheet credit exposures before adoption of CECL | $ 12,500,000 |

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- Definition Off balance sheet credit exposure before adoption of credit losses effect of change in method. + References No definition available. + Details
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Namespace Prefix: | nycb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121611286&loc=d3e11927-110247 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=121599878&loc=SL82919202-210446 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
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