Investments (Details 19) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fixed maturity securities [Member]
Gross unrealized loss greater than $10 million for fixed maturity and equity securities
Number of securities	37	96
Total gross unrealized loss	$ 676	$ 1,703
Percentage of total gross unrealized loss	30.00%	31.00%
Equity Securities [Member]
Gross unrealized loss greater than $10 million for fixed maturity and equity securities
Number of securities	5	8
Total gross unrealized loss	$ 87	$ 117
Percentage of total gross unrealized loss	44.00%	39.00%

This item represents the gross unrealized losses greater than a stated monetary amount for securities at the end of the period which are categorized neither as held-to-maturity nor trading securities. Such gross unrealized losses are the excess of the carrying value of the Available-for-sale Securities over their fair value as of the reporting date. Such gross unrealized losses are included in other comprehensive income in the statement of shareholders' equity, unless the Available-for-sale Security is designated as a hedge. All or a portion of the unrealized holding loss of an available-for-sale security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge.

No definition available.

Name:	met_GrossUnrealizedLossesAvailableForSaleSecuritiesGreaterThanStatedMonetaryAmount
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant