Investments (Details 27) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Securities on loan:
Cost or amortized cost	$ 25,336	$ 23,715
Estimated fair value	25,938	24,230
Aging of cash collateral liability:
Open	3,477	2,752
Less than thirty days	15,609	12,301
Thirty days or greater but less than sixty days	5,351	4,399
Sixty days or greater but less than ninety days	1,020	2,291
Ninety Days Or Greater Aging Of Cash Collateral Liability Securities Lending	1,124	2,904
Total cash collateral liability	26,581	24,647
Security collateral on deposit from counterparties	22	0
Reinvestment portfolio - estimated fair value	$ 26,482	$ 24,177

Aging Of Cash Collateral Liability Abstract.

Name:	met_AgingOfCashCollateralLiabilityAbstract
Namespace Prefix:	met
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total cash collateral liability for securities loaned.

+ Details

Name:	met_CashCollateralLiability
Namespace Prefix:	met
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the cash collateral liability amount related to loaned securities that could be returned to the Company over the next 2 - 29 business days from the stated date requiring the Company to immediately return the cash collateral.

+ Details

Name:	met_LessThanThirtyDaysAgingOfCashCollateralLiabilitySecuritiesLending
Namespace Prefix:	met
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the cash collateral liability amount related to loaned securities that could be returned to the Company 90 business days or greater from the stated date requiring the Company to immediately return the cash collateral.

+ Details

Name:	met_NinetyDaysOrGreaterAgingOfCashCollateralLiabilitySecuritiesLending
Namespace Prefix:	met
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the cash collateral liability amount related to loaned securities in the open category. Open means that the related loaned security could be returned to the Company on the next business day requiring the Company to immediately return the cash collateral.

+ Details

Name:	met_OpenCashCollateralLiabilitySecuritiesLending
Namespace Prefix:	met
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the estimated fair value of the securities lending reinvestment portfolio.

+ Details

Name:	met_SecuritiesLendingReinvestmentPortfolioEstimatedFairValue
Namespace Prefix:	met
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The fair value as of the balance sheet date of securities loaned to other broker dealers, typically used by such parties to cover short sales, secured by cash or other securities furnished by such parties until the borrowing is closed.

+ Details

Name:	met_SecuritiesLoanedEstimatedFairValue
Namespace Prefix:	met
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Securities On Loan Abstract.

+ Details

Name:	met_SecuritiesOnLoanAbstract
Namespace Prefix:	met
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The fair value as of the balance sheet date of securities held that had been pledged by counterparties under securities lending program.

+ Details

Name:	met_SecurityCollateralOnDepositFromCounterparties
Namespace Prefix:	met
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the cash collateral liability amount related to loaned securities that could be returned to the Company over the next 60 - 89 business days from the stated date requiring the Company to immediately return the cash collateral.

+ Details

Name:	met_SixtyDaysOrGreaterButLessThanNinetyDaysAgingOfCashCollateralLiabilitySecuritiesLending
Namespace Prefix:	met
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the cash collateral liability amount related to loaned securities that could be returned to the Company over the next 30 - 59 business days from the stated date requiring the Company to immediately return the cash collateral.

+ Details

Name:	met_ThirtyDaysOrGreaterButLessThanSixtyDaysAgingOfCashCollateralLiabilitySecuritiesLending
Namespace Prefix:	met
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of securities loaned to other broker dealers, typically used by such parties to cover short sales, secured by cash or other securities furnished by such parties until the borrowing is closed.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 140
-Paragraph 17
-Subparagraph a

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Audit and Accounting Guide (AAG)
-Number AAG-BRD
-Chapter 4
-Paragraph 32
-IssueDate 2006-05-01

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 140
-Paragraph 91, 93

+ Details

Name:	us-gaap_SecuritiesLoaned
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant