Insurance (Obligations Under Funding Agreements - Narrative) (Details) - USD ($) $ in Billions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Insurance [Abstract]
Funding agreements issued to certain SPEs	$ 40.4	$ 37.3	$ 41.8
Funding agreements repaid to certain SPEs	36.7	36.4	$ 43.7
Outstanding funding agreements to certain SPEs	$ 39.9	$ 34.6

Amount of funding agreements issued during current year to certain special purpose entities that have issued debt securities for which payment of interest and principal is secured by such funding agreements.

No definition available.

Name:	met_FundingAgreementsIssuedToCertainSpecialPurposeEntities
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration