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Investments (Fixed Maturity and Equity Securities Available-For-Sale by Sector) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Available-for-sale Securities [Abstract]      
Amortized Cost $ 173,604us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis $ 165,371us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis  
Cost or Amortized Cost 1,926us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis 1,813us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis  
Gross Unrealized OTTI Loss 66mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss 149mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss 256mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $173,604 and $165,371, respectively; includes $160 and $157, respectively, relating to variable interest entities) 188,911us-gaap_AvailableForSaleSecuritiesDebtSecurities 173,746us-gaap_AvailableForSaleSecuritiesDebtSecurities  
Equity securities 2,065us-gaap_AvailableForSaleSecuritiesEquitySecurities 1,892us-gaap_AvailableForSaleSecuritiesEquitySecurities  
Fixed maturity securities      
Available-for-sale Securities [Abstract]      
Amortized Cost 173,604us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
165,371us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
 
Gross Unrealized Gain 16,672mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
10,953mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
 
Gross Unrealized Temporary Loss 1,299mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
2,429mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
 
Gross Unrealized OTTI Loss 66mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
149mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
 
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $173,604 and $165,371, respectively; includes $160 and $157, respectively, relating to variable interest entities) 188,911us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
173,746us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
 
U.S. corporate      
Available-for-sale Securities [Abstract]      
Amortized Cost 59,532us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
60,244us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
 
Gross Unrealized Gain 6,246mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
4,678mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
 
Gross Unrealized Temporary Loss 421mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
693mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
 
Gross Unrealized OTTI Loss 0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
 
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $173,604 and $165,371, respectively; includes $160 and $157, respectively, relating to variable interest entities) 65,357us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
64,229us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
 
U.S. Treasury and agency      
Available-for-sale Securities [Abstract]      
Amortized Cost 34,391us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
29,508us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Gross Unrealized Gain 4,698mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
1,730mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Gross Unrealized Temporary Loss 19mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
694mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Gross Unrealized OTTI Loss 0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $173,604 and $165,371, respectively; includes $160 and $157, respectively, relating to variable interest entities) 39,070us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
30,544us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Foreign corporate      
Available-for-sale Securities [Abstract]      
Amortized Cost 28,395us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
27,082us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
 
Gross Unrealized Gain 1,934mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
1,959mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
 
Gross Unrealized Temporary Loss 511mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
285mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
 
Gross Unrealized OTTI Loss 0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
 
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $173,604 and $165,371, respectively; includes $160 and $157, respectively, relating to variable interest entities) 29,818us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
28,756us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember
 
RMBS      
Available-for-sale Securities [Abstract]      
Amortized Cost 26,893us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
24,119us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Gross Unrealized Gain 1,493mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
1,109mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Gross Unrealized Temporary Loss 157mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
368mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Gross Unrealized OTTI Loss 66mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
150mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $173,604 and $165,371, respectively; includes $160 and $157, respectively, relating to variable interest entities) 28,163us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
24,710us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
CMBS      
Available-for-sale Securities [Abstract]      
Amortized Cost 7,705us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
8,203us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
 
Gross Unrealized Gain 241mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
262mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
 
Gross Unrealized Temporary Loss 33mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
89mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
 
Gross Unrealized OTTI Loss 0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
 
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $173,604 and $165,371, respectively; includes $160 and $157, respectively, relating to variable interest entities) 7,913us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
8,376us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
 
ABS      
Available-for-sale Securities [Abstract]      
Amortized Cost 8,206us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
7,789us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
 
Gross Unrealized Gain 102mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
151mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
 
Gross Unrealized Temporary Loss 82mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
117mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
 
Gross Unrealized OTTI Loss 0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
(1)mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
 
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $173,604 and $165,371, respectively; includes $160 and $157, respectively, relating to variable interest entities) 8,226us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
7,824us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
 
State and political subdivision      
Available-for-sale Securities [Abstract]      
Amortized Cost 5,329us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
5,386us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Gross Unrealized Gain 1,197mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
467mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Gross Unrealized Temporary Loss 6mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
76mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Gross Unrealized OTTI Loss 0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $173,604 and $165,371, respectively; includes $160 and $157, respectively, relating to variable interest entities) 6,520us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
5,777us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
 
Foreign government      
Available-for-sale Securities [Abstract]      
Amortized Cost 3,153us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
3,040us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Gross Unrealized Gain 761mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
597mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Gross Unrealized Temporary Loss 70mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
107mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Gross Unrealized OTTI Loss 0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
0mlic_OtherThanTemporaryImpairmentsOnDebtSecuritiesTransferredToOtherComprehensiveIncomeLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $173,604 and $165,371, respectively; includes $160 and $157, respectively, relating to variable interest entities) 3,844us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
3,530us-gaap_AvailableForSaleSecuritiesDebtSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
 
Equity securities      
Available-for-sale Securities [Abstract]      
Cost or Amortized Cost 1,926us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
1,813us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
 
Gross Unrealized Gain 195mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
159mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
 
Gross Unrealized Temporary Loss 56mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
80mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
 
Gross Unrealized OTTI Loss 0mlic_OtherThanTemporaryImpairmentsOnEquitySecuritiesTransferredToOtherComprehensiveLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
0mlic_OtherThanTemporaryImpairmentsOnEquitySecuritiesTransferredToOtherComprehensiveLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
 
Equity securities 2,065us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
1,892us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
 
Common stock      
Available-for-sale Securities [Abstract]      
Cost or Amortized Cost 1,236us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
1,070us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
 
Gross Unrealized Gain 142mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
97mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
 
Gross Unrealized Temporary Loss 26mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
3mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
 
Gross Unrealized OTTI Loss 0mlic_OtherThanTemporaryImpairmentsOnEquitySecuritiesTransferredToOtherComprehensiveLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
0mlic_OtherThanTemporaryImpairmentsOnEquitySecuritiesTransferredToOtherComprehensiveLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
 
Equity securities 1,352us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
1,164us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
 
Non-redeemable preferred stock      
Available-for-sale Securities [Abstract]      
Cost or Amortized Cost 690us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_NonredeemablePreferredStockMember
743us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_NonredeemablePreferredStockMember
 
Gross Unrealized Gain 53mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_NonredeemablePreferredStockMember
62mlic_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_NonredeemablePreferredStockMember
 
Gross Unrealized Temporary Loss 30mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_NonredeemablePreferredStockMember
77mlic_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
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Gross Unrealized OTTI Loss 0mlic_OtherThanTemporaryImpairmentsOnEquitySecuritiesTransferredToOtherComprehensiveLoss
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0mlic_OtherThanTemporaryImpairmentsOnEquitySecuritiesTransferredToOtherComprehensiveLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
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Equity securities $ 713us-gaap_AvailableForSaleSecuritiesEquitySecurities
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$ 728us-gaap_AvailableForSaleSecuritiesEquitySecurities
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