Commitments and Contingencies - Off Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Other Commitments [Line Items]
Commercial, performance stand-by, and financial stand-by letters of credit	$ 776	$ 803
Total commitments	13,256	13,843
Total loan commitments
Other Commitments [Line Items]
Total loan commitments	12,480	13,040
Multi-family and Commercial real estate
Other Commitments [Line Items]
Total loan commitments	2,176	2,478
One-to-four family including interest rate locks
Other Commitments [Line Items]
Total loan commitments	547	725
Other loan commitments
Other Commitments [Line Items]
Total loan commitments	$ 9,757	$ 9,837

Other Commitments And Guarantor Obligations, Maximum Exposure, Undiscounted

No definition available.

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Namespace Prefix:	fbc_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

+ Details

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- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

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- 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

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- Details

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- Details

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- Details

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- Details

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