Fair Value Measurements - Differences Between Aggregate Fair Value and Aggregate Remaining Contractual Principal Balance Outstanding (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, unpaid principal balance (UPB)	$ 3,239	$ 4,828
Total assets at fair value	3,175	4,936
Assets, fair value over/(under) UPB	(64)	108
Nonaccrual loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, unpaid principal balance (UPB)	39	33
Total assets at fair value	34	29
Assets, fair value over/(under) UPB	(5)	(4)
Other performing loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, unpaid principal balance (UPB)	3,200	4,795
Total assets at fair value	3,141	4,907
Assets, fair value over/(under) UPB	(59)	112
Loans held-for-sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, unpaid principal balance (UPB)	3,213	4,808
Total assets at fair value	3,154	4,920
Assets, fair value over/(under) UPB	(59)	112
Loans held-for-sale \| Nonaccrual loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, unpaid principal balance (UPB)	25	18
Total assets at fair value	23	16
Assets, fair value over/(under) UPB	(2)	(2)
Loans held-for-sale \| Other performing loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, unpaid principal balance (UPB)	3,188	4,790
Total assets at fair value	3,131	4,904
Assets, fair value over/(under) UPB	(57)	114
Loans held-for-investment
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, unpaid principal balance (UPB)	26	20
Total assets at fair value	21	16
Assets, fair value over/(under) UPB	(5)	(4)
Loans held-for-investment \| Nonaccrual loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, unpaid principal balance (UPB)	14	15
Total assets at fair value	11	13
Assets, fair value over/(under) UPB	(3)	(2)
Loans held-for-investment \| Other performing loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, unpaid principal balance (UPB)	12	5
Total assets at fair value	10	3
Assets, fair value over/(under) UPB	$ (2)	$ (2)

This item represents aggregate unpaid principal balance of assets that have contractual principal amounts and for which the fair value option has been elected.

No definition available.

+ Details

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

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

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- Definition

For loans held as assets for which the fair value option has been elected, this item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of those loans that are 90 days or more past due, in nonaccrual status, or both.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(3)
-URI http://asc.fasb.org/extlink&oid=123596393&loc=d3e14064-108612

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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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