Cash received (paid) in connection with the change in market value of collateral used to secure debt.

No definition available.

Name:	met_CashReceivedPaidInConnectionWithCollateralFinancingArrangements
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Collateral Financing Arrangements.

+ References

No definition available.

+ Details

Name:	met_CollateralFinancingArrangementsTextualsAbstract
Namespace Prefix:	met_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Term in Years.

+ References

No definition available.

+ Details

Name:	met_DebtInstrumentTermInYears
Namespace Prefix:	met_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The element presents the invested assets on deposit, held in trust and pledged as collateral.

+ References

No definition available.

+ Details

Name:	met_InvestedAssetsOnDepositHeldInTrustAndPledgedAsCollateral
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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

- Definition

Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

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

- Definition

Amount of increase (decrease) in receivables classified as other.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

+ Details

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

- Definition

Amount of the cost of borrowed funds accounted for as interest expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.9)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

Name:	us-gaap_InterestExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_ConsolidatedEntitiesAxis=us-gaap_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=met_MetLifeReinsuranceCompanyOfCharlestonMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=met_CashReceivedPaidCollateralFinancingArrangementsMRCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=met_SecuredDebtMrcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	met_CumulativeRepaymentAxis=met_CumulativeRepaymentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	met_TransferAssetsHeldInTrustAxis=met_TransferAssetsHeldInTrustMember
Namespace Prefix:
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Period Type:

Collateral Financing Arrangements (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2007
Collateral Financing Arrangements (Textuals) [Abstract]
Debt Instrument, Face Amount		$ 3,200	$ 3,200
Parent Company
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	six-month LIBOR plus 1.00%
Collateral Financing Arrangements (Textuals) [Abstract]
Interest expense		1,108	1,152	$ 1,171
MRC [Member] \| Secured Debt [Member]
Collateral Financing Arrangements (Textuals) [Abstract]
Interest expense		30	24	20
Debt Instrument, Face Amount					$ 2,500
Debt Instrument, Term in Years					35 years
Debt Instrument, Basis Spread on Variable Rate					0.55%
Partial repurchase		153	68	57
Increase (Decrease) in Other Receivables		20	0	8
Invested Assets On Deposit Held In Trust And Pledged As Collateral		1,248	1,211
MRC [Member] \| Cash Received (Paid) Collateral Financing Arrangements MRC [Member]
Collateral Financing Arrangements (Textuals) [Abstract]
Cash Received (Paid) In Connection With Collateral Financing Arrangements		$ 20	8	8
MRC [Member] \| Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms		3-month LIBOR plus 0.55%
MRC [Member] \| Parent Company \| Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms		3-month LIBOR plus 1.12%
Collateral Financing Arrangements (Textuals) [Abstract]
Debt Instrument, Basis Spread on Variable Rate					1.12%
Cumulative Repayment [Member] \| MRC [Member] \| Secured Debt [Member]
Collateral Financing Arrangements (Textuals) [Abstract]
Partial repurchase		$ 1,400
Transfer Assets Held In Trust [Member] \| Secured Debt [Member]
Collateral Financing Arrangements (Textuals) [Abstract]
Invested Assets On Deposit Held In Trust And Pledged As Collateral		$ 3	$ 1	$ 30