Investments (Details Textuals 17) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Investments [Abstract]
Increase (decrease) in estimated fair value of derivatives related to economic hedges in equity method international joint investments that do not qualify for hedge accounting	$ 0	$ 0	$ 0	$ (23)

Increase (decrease) in estimated fair value of derivatives related to economic hedges in equity method international joint investments that do not qualify for hedge accounting.

No definition available.

Name:	met_IncreaseDecreaseInEstimatedFairValueOfDerivativesRelatedToEconomicHedgesInEquityMethodInternationalJointInvestmentsThatDoNotQualifyForHedgeAccounting
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration