Fair Value (Transfers Between Levels) (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value Disclosures [Abstract]
Fair Value Assets And Liabilities Transferred Between Levels 1 And Levels 2	$ 160	$ 101

Amount of transfers of assets and liabilites measured on a recurring basis between Levels 1 and Levels 2 of the fair value hierarchy.

No definition available.

Name:	met_FairValueAssetsAndLiabilitiesTransferredBetweenLevels1AndLevels2
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant