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Investments (Net Investment Gains Losses - Narrative) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]    
Non-investment portfolio gains (losses) $ 23us-gaap_GainLossOnSaleOfInvestments $ (4)us-gaap_GainLossOnSaleOfInvestments
Gains (losses) from foreign currency transactions 161us-gaap_ForeignCurrencyTransactionGainLossRealized 5us-gaap_ForeignCurrencyTransactionGainLossRealized
MetLife Assurance Limited    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]    
Non-investment portfolio gains (losses)   $ 495us-gaap_GainLossOnSaleOfInvestments
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= met_MetlifeAssuranceLimitedMember