Fair Value (Details 6) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value [Abstract]
Contractual principal balance	$ 0	$ 6,914
Difference between estimated fair value and contractual principal balance	0	712
Liability related to securitized reverse residential mortgage loans	$ 0	$ 7,626

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