Investments (Details 37) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	$ 516	$ 539
Interest Income Recognized - Cash Basis	4	5
Interest Income Recognized - Accrual Basis	0	1
Commercial mortgage loans portfolio segment [Member]
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	273	242
Interest Income Recognized - Cash Basis	3	3
Interest Income Recognized - Accrual Basis	0	1
Agricultural mortgage loans portfolio segment [Member]
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	229	278
Interest Income Recognized - Cash Basis	1	2
Interest Income Recognized - Accrual Basis	0	0
Residential mortgage loans portfolio segment [Member]
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	14	19
Interest Income Recognized - Cash Basis	0	0
Interest Income Recognized - Accrual Basis	$ 0	$ 0

Name:	met_DisclosureOfAverageInvestmentAndRelatedInterestIncomeInImpairedMortgageLoansHeldForInvestmentAbstract
Namespace Prefix:	met_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The average recorded investment related to impaired financing receivables.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=6965416&loc=d3e5212-111524

-Subparagraph (c)(1)

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=6965416&loc=d3e5258-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The interest income recognized during the time within that period that the financing receivables were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The interest income recognized on a cash-basis method of accounting during the time within that period that the financing receivables were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration