Allowance For Loan Losses [Abstract]

No definition available.

Name:	fbc_AllowanceForLoanLossesAbstract
Namespace Prefix:	fbc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Loans Held-For-Investment [Abstract]

+ References

No definition available.

+ Details

Name:	fbc_LoansHeldForInvestmentAbstract
Namespace Prefix:	fbc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118955202&loc=SL82895884-210446

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7)(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

+ Details

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

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

+ Details

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, before allowance for credit loss, of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919230-210447

+ Details

Name:	us-gaap_NotesReceivableGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_FirstMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbc_ConsumerOtherFinancingReceivable1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbc_CommercialRealEstateLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbc_CommercialAndIndustrialLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_WarehouseAgreementBorrowingsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans Held-for-Investment - Method of Evaluation by Class of Loan (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Loans held-for-investment
Individually evaluated	$ 92		$ 55
Collectively evaluated	11,553		9,023
Total loans	11,645		9,078
Allowance for loan losses
Individually evaluated	11		11
Collectively evaluated	99		117
Total allowance for loan losses	110	$ 127	128	$ 137	$ 139	$ 140
Residential first mortgage
Loans held-for-investment
Individually evaluated	33		32
Collectively evaluated	3,201		2,959
Total loans	3,234		2,991
Allowance for loan losses
Individually evaluated	3		4
Collectively evaluated	23		34
Total allowance for loan losses	26	35	38	45	47	47
Home equity
Loans held-for-investment
Individually evaluated	21		23
Collectively evaluated	898		706
Total loans	919		729
Allowance for loan losses
Individually evaluated	7		7
Collectively evaluated	9		8
Total allowance for loan losses	16	16	15	19	21	22
Other Consumer
Loans held-for-investment
Individually evaluated	1		0
Collectively evaluated	575		314
Total loans	576		314
Allowance for loan losses
Individually evaluated	1		0
Collectively evaluated	4		3
Total allowance for loan losses	5	4	3	1	1	1
Commercial real estate
Loans held-for-investment
Individually evaluated	0		0
Collectively evaluated	2,463		2,152
Total loans	2,463		2,152
Allowance for loan losses
Individually evaluated	0		0
Collectively evaluated	35		48
Total allowance for loan losses	35	36	48	45	44	45
Commercial and industrial
Loans held-for-investment
Individually evaluated	37		0
Collectively evaluated	1,784		1,433
Total loans	1,821		1,433
Allowance for loan losses
Individually evaluated	0		0
Collectively evaluated	23		18
Total allowance for loan losses	23	30	18	21	20	19
Warehouse lending
Loans held-for-investment
Individually evaluated	0		0
Collectively evaluated	2,632		1,459
Total loans	2,632		1,459
Allowance for loan losses
Individually evaluated	0		0
Collectively evaluated	5		6
Total allowance for loan losses	$ 5	$ 6	$ 6	$ 6	$ 6	$ 6