Investments (Repurchase Agreement - Narrative) (Details) - Jun. 30, 2015 - USD ($) $ in Millions	Total
Offsetting Assets [Line Items]
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	$ 217
Receivable Under Reverse Repurchase Agreements	499
Payable Under Repurchase Agreements	499
Amount Offset in Balance Sheet	499
Maximum
Offsetting Assets [Line Items]
Net Amount Assets (Liabilities) From Repurchase, Reverse Repurchase Agreements	$ 1
Fixed Maturity Securities
Offsetting Assets [Line Items]
Percentage of Estimated Fair Value of Securities Loaned at Inception Based on Collateral Obtained	95.00%
Percentage of Estimated Fair Value of Borrowed Securities at Inception Based on Pledged Cash Collateral	98.00%
Securities Loaned, Not Subject to Master Netting Arrangement	$ 518
Securities Borrowed, Not Subject to Master Netting Arrangement	506
Corporate fixed maturity securities
Offsetting Assets [Line Items]
Payable Under Repurchase Agreements	$ 499

Amount offset in balance sheet from receivables and payables under repurchase and reverse repurchase agreement.

No definition available.

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

- Definition

Net amount, after affects of netting, from repurchase and reverse repurchase agreements presented on the Balance sheet.

+ References

No definition available.

+ Details

Name:	met_NetAmountAssetsLiabilitiesFromRepurchaseReverseRepurchaseAgreements
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The gross amounts payable under repurchase agreement.

+ References

No definition available.

+ Details

Name:	met_PayableUnderRepurchaseAgreements
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The percentage of the estimated fair value of borrowed securities at inception based on pledged cash collateral.

+ References

No definition available.

+ Details

Name:	met_PercentageofEstimatedFairValueofBorrowedSecuritiesatInceptionBasedonPledgedCashCollateral
Namespace Prefix:	met_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of the estimated fair value of securities loaned at inception based on collateral obtained.

+ References

No definition available.

+ Details

Name:	met_PercentageofEstimatedFairValueofSecuritiesLoanedatInceptionBasedonCollateralObtained
Namespace Prefix:	met_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The gross amounts of those recognized receivable under reverse repurchase agreements.

+ References

No definition available.

+ Details

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

- Definition

Fair value of the collateral, or portion thereof, that has been re-pledged, delivered, or otherwise used.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=55761124&loc=SL6224234-111729

+ Details

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

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

- Definition

Amount of securities borrowed from entities in exchange for collateral, not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 22

-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226052-175313

+ Details

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

- Definition

Amount of securities loaned to entities in exchange for collateral, not subject to a master netting arrangement.

+ References

+ Details

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

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_DebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: