Fair Value (Details 5) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fair Value [Abstract]
Contractual principal balance	$ 6,914
Excess of estimated fair value over contractual principal balance	712
Liability related to securitized reverse residential mortgage loans	$ 7,626	$ 0

This item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of the liability related to securitized reverse residential mortgage loans that have contractual principal amounts and for which the fair value option has been elected.

No definition available.

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