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Future Policy Benefits - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2022
Insurance [Abstract] |  |
Liability for Future Policy Benefit, Adverse Development, Expense, Loss At Issue | $ 147 | $ 99
Liability for Future Policy Benefit, Adverse Development, Expense, Loss at Issue, Net Remeasurement Loss |  | $ 31

X
- Definition Amount of expense for adverse development on liability of future policy benefit from net premium exceeding gross premium for loss at issue. + References No definition available. + Details
Name: | met_LiabilityForFuturePolicyBenefitAdverseDevelopmentExpenseLossAtIssue
Namespace Prefix: | met_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of expense for adverse development on liability of future policy benefit from net premium exceeding gross premium for net remeasurement loss. + References No definition available. + Details
Name: | met_LiabilityForFuturePolicyBenefitAdverseDevelopmentExpenseNetRemeasurementLoss
Namespace Prefix: | met_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_InsuranceAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration