Future Policy Benefits - Narrative (Details) $ in Millions	9 Months Ended
Sep. 30, 2024 USD ($)
Insurance [Abstract]
Liability for Future Policy Benefit, Adverse Development, Expense, Loss At Issue	$ 129

Amount of expense for adverse development on liability of future policy benefit from net premium exceeding gross premium for loss at issue.

No definition available.

Name:	met_LiabilityForFuturePolicyBenefitAdverseDevelopmentExpenseLossAtIssue
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration