Investments (Details Textuals 10) (USD $) In Billions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Investments [Abstract]
Concentration of Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale	$ 5.8	$ 6.8

Gross unrealized losses related to fixed maturity and equity securities, including the portion of OTTI loss on fixed maturity securities recognized in accumulated other comprehensive income (loss).

No definition available.

Name:	met_ConcentrationOfGrossUnrealizedLossAndOttiLossForDebtAndEquitySecuritiesAvailableForSale
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant