Business Basis of Presentation and Summary of Significant Accounting Policies (Textuals)	3 Months Ended
Mar. 31, 2012 Segment
Business, Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Number of segments	6

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

No definition available.

Name:	met_NumberOfReportableSegments
Namespace Prefix:	met_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration