Investments (Changes in Fixed Maturity Securities with Noncredit OTTI Losses - Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Noncredit OTTI losses on fixed maturity securities, net of DAC, included in accumulated other comprehensive income (loss)	$ 47	$ (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.

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