Investments (Details Textuals 12) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012
Investments [Abstract]
Increase Decrease In Debt Securities And Equity Securities With Gross Unrealized Loss Greater Than Ten Million Dollars	$ (613)
Fixed maturity and equity securities available-for-sale investment disclosure with gross unrealized loss of greater than stated monetary value	$ 10

This caption represents the increase (decrease) in gross unrealized loss for fixed maturity and equity securities available-for-sale with a gross unrealized loss greater than $10 million.

No definition available.

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