Investments (Changes in Fixed Maturity Securities with Noncredit OTTI Losses - Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2013	Dec. 31, 2012
Investments [Abstract]
Noncredit OTTI losses on fixed maturity securities, net of DAC, included in accumulated other comprehensive income (loss)	$ 24	$ (21)

This item presents the noncredit OTTI losses on fixed maturity securities, net of deferred acquisition costs, recognized during the reporting period included in accumulated other comprehensive loss.

No definition available.

Name:	met_NonCreditOttiLossesOnDebtSecuritiesRecognizedNetOfDacIncludedInAccumulatedOtherComprehensiveIncomeLoss
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration