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Investments (Past Due and Interest Accrual Status of Mortgage Loans) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Past Due and Interest Accrual Status of Mortgage Loans    
Past Due $ 184us-gaap_FinancingReceivableRecordedInvestmentPastDue $ 135us-gaap_FinancingReceivableRecordedInvestmentPastDue
Nonaccrual Status 279us-gaap_LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest 303us-gaap_LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest
Commercial    
Past Due and Interest Accrual Status of Mortgage Loans    
Past Due 10us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialLoanMember		 12us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialLoanMember
Nonaccrual Status 75us-gaap_LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialLoanMember		 191us-gaap_LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialLoanMember
Agricultural    
Past Due and Interest Accrual Status of Mortgage Loans    
Past Due 1us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= met_AgriculturalPortfolioSegmentMember		 44us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= met_AgriculturalPortfolioSegmentMember
Nonaccrual Status 41us-gaap_LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= met_AgriculturalPortfolioSegmentMember		 47us-gaap_LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= met_AgriculturalPortfolioSegmentMember
Residential    
Past Due and Interest Accrual Status of Mortgage Loans    
Past Due 173us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialPortfolioSegmentMember		 79us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialPortfolioSegmentMember
Nonaccrual Status $ 163us-gaap_LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialPortfolioSegmentMember		 $ 65us-gaap_LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialPortfolioSegmentMember