Employee Benefit Plans (Details Textuals) (United States Pension Plans of US Entity, Defined Benefit [Member])	3 Months Ended
Mar. 31, 2012
United States Pension Plans of US Entity, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Subsidiaries issuance of group annuity and life insurance contracts supporting employee benefit plan assets primarily invested in separate accounts sponsored by subsidiaries	99.00%

Subsidiaries Issuance of Group Annuity And Life Insurance Contracts Supporting Employee Benefit Plan Assets Sponsored By Subsidiaries.

No definition available.

Name:	met_SubsidiariesIssuanceOfInsuranceContractsSupportingEmployeeBenefitPlanAssets
Namespace Prefix:	met_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration