Investments (Details Textuals 11) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Investments [Abstract]
Fixed maturity and equity securities with gross unrealized loss greater than $10 million	$ 10	$ 10

Investment disclosure of fixed maturity and equity securities with gross unrealized loss greater than stated monetary amount. Disclosure includes the number of securities, total gross unrealized loss and percentage of total gross unrealized loss.

No definition available.

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