Employee Benefit Plans (Assumed Healthcare Cost Trend Rates) (Details)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Assumed healthcare costs trend rates
Healthcare costs trend rate	6.40%	6.40%
Factors, Pre-Medicare
Assumed healthcare costs trend rates
Year that rate reaches ultimate trend rate - Pre-Medicare	2094	2094
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.40%	4.40%
Factors, Post-Medicare
Assumed healthcare costs trend rates
Year that rate reaches ultimate trend rate - Pre-Medicare	2089	2094
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.70%	4.60%

Name:	us-gaap_DefinedBenefitPlanAssumedHealthCareCostTrendRatesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (l)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Health Care Cost Trend Rate

-URI http://asc.fasb.org/extlink&oid=6514820

+ Details

Name:	us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The ultimate trend rate for health care costs.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Year the ultimate health care cost trend rate is expected to be reached, in CCYY format.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanYearThatRateReachesUltimateTrendRate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	met_DefinedBenefitPlanAssumedHealthCareCostTrendRatesAxis=met_DefinedBenefitPlanAssumedHealthCareCostTrendRatesFactorsPostMedicareMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	met_DefinedBenefitPlanAssumedHealthCareCostTrendRatesAxis=met_DefinedBenefitPlanAssumedHealthCareCostTrendRatesFactorsPreMedicareMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: