Investments (Details Textuals 13)	Dec. 31, 2011
Investments [Abstract]
Equity securities available-for-sale with gross unrealized loss of equal to or greater than stated percentage	20.00%

Investment disclosure of equity securities available-for-sale with gross unrealized loss of equal to or greater than stated percentage.

No definition available.

Name:	met_PercentageAratedOrBetterWithGrossUnrealizedLossOfTwentyPercentOrMore
Namespace Prefix:	met_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant