Fair Value (Financial Instruments Carried at Other Than Fair Value) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets
Policy loans	$ 11,782	$ 11,884
Liabilities
Collateral financing arrangements	4,196	4,196
Junior subordinated debt securities	3,193	3,192
Separate account liabilities	255,250	235,393
Estimated Fair Value [Member]
Assets
Mortgages held-for-investment	57,639	57,381
Held-for-sale	225	365
Mortgage loans, net	57,864	57,746
Policy loans	13,601	14,257
Real estate joint ventures	177	171
Other Limited Partnership Interests	1,171	1,277
Other invested assets	855	815
Premiums, reinsurance and other receivables	4,546	3,705
Other assets	305	292
Liabilities
Policyholder account balances	147,010	158,040
Bank deposits	0	6,416
Long-term Debt, Fair Value	17,889	18,978
Collateral financing arrangements	3,947	3,839
Junior subordinated debt securities	3,738	3,984
Other Liabilities	3,431	1,916
Separate account liabilities	62,984	58,726
Estimated Fair Value [Member] \| Mortgage Loan Commitments [Member]
Assets
Off-balance sheet commitments		12
Liabilities
Off-balance sheet commitments	(14)
Estimated Fair Value [Member] \| Commitments to Fund Bank Credit Facilities, Bridge Loans and Private Corporate Bond Investments [Member]
Assets
Off-balance sheet commitments		22
Liabilities
Off-balance sheet commitments	(1)
Estimated Fair Value [Member] \| Level 1 [Member]
Assets
Mortgages held-for-investment	0	0
Held-for-sale	0	0
Mortgage loans, net	0	0
Policy loans	0	0
Real estate joint ventures	0	0
Other Limited Partnership Interests	0	0
Other invested assets	234	305
Premiums, reinsurance and other receivables	0	0
Other assets	0	0
Liabilities
Policyholder account balances	0	0
Bank deposits	0	0
Long-term Debt, Fair Value	0	0
Collateral financing arrangements	0	0
Junior subordinated debt securities	0	0
Other Liabilities	0	0
Separate account liabilities	0	0
Estimated Fair Value [Member] \| Level 1 [Member] \| Mortgage Loan Commitments [Member]
Assets
Off-balance sheet commitments		0
Liabilities
Off-balance sheet commitments	0
Estimated Fair Value [Member] \| Level 1 [Member] \| Commitments to Fund Bank Credit Facilities, Bridge Loans and Private Corporate Bond Investments [Member]
Assets
Off-balance sheet commitments		0
Liabilities
Off-balance sheet commitments	0
Estimated Fair Value [Member] \| Level 2 [Member]
Assets
Mortgages held-for-investment	0	0
Held-for-sale	0	0
Mortgage loans, net	0	0
Policy loans	1,701	1,690
Real estate joint ventures	0	0
Other Limited Partnership Interests	0	0
Other invested assets	276	144
Premiums, reinsurance and other receivables	2,080	745
Other assets	211	214
Liabilities
Policyholder account balances	0	0
Bank deposits	0	2,018
Long-term Debt, Fair Value	17,889	18,978
Collateral financing arrangements	0	0
Junior subordinated debt securities	3,738	3,984
Other Liabilities	2,161	673
Separate account liabilities	62,984	58,726
Estimated Fair Value [Member] \| Level 2 [Member] \| Mortgage Loan Commitments [Member]
Assets
Off-balance sheet commitments		0
Liabilities
Off-balance sheet commitments	0
Estimated Fair Value [Member] \| Level 2 [Member] \| Commitments to Fund Bank Credit Facilities, Bridge Loans and Private Corporate Bond Investments [Member]
Assets
Off-balance sheet commitments		22
Liabilities
Off-balance sheet commitments	(1)
Estimated Fair Value [Member] \| Level 3 [Member]
Assets
Mortgages held-for-investment	57,639	57,381
Held-for-sale	225	365
Mortgage loans, net	57,864	57,746
Policy loans	11,900	12,567
Real estate joint ventures	177	171
Other Limited Partnership Interests	1,171	1,277
Other invested assets	345	366
Premiums, reinsurance and other receivables	2,466	2,960
Other assets	94	78
Liabilities
Policyholder account balances	147,010	158,040
Bank deposits	0	4,398
Long-term Debt, Fair Value	0	0
Collateral financing arrangements	3,947	3,839
Junior subordinated debt securities	0	0
Other Liabilities	1,270	1,243
Separate account liabilities	0	0
Estimated Fair Value [Member] \| Level 3 [Member] \| Mortgage Loan Commitments [Member]
Assets
Off-balance sheet commitments		12
Liabilities
Off-balance sheet commitments	(14)
Estimated Fair Value [Member] \| Level 3 [Member] \| Commitments to Fund Bank Credit Facilities, Bridge Loans and Private Corporate Bond Investments [Member]
Assets
Off-balance sheet commitments		0
Liabilities
Off-balance sheet commitments	0
Carrying Value [Member]
Assets
Mortgages held-for-investment	55,200	53,926
Held-for-sale	225	365
Mortgage loans, net	55,425	54,291
Policy loans	11,782	11,884
Real estate joint ventures	107	113
Other Limited Partnership Interests	1,013	1,154
Other invested assets	855	815
Premiums, reinsurance and other receivables	4,470	3,287
Other assets	276	260
Liabilities
Policyholder account balances	140,721	149,928
Bank deposits	0	6,416
Long-term Debt, Fair Value	16,275	16,502
Collateral financing arrangements	4,196	4,196
Junior subordinated debt securities	3,193	3,192
Other Liabilities	3,428	1,913
Separate account liabilities	62,984	58,726
Carrying Value [Member] \| Mortgage Loan Commitments [Member]
Assets
Off-balance sheet commitments		0
Liabilities
Off-balance sheet commitments	0
Carrying Value [Member] \| Commitments to Fund Bank Credit Facilities, Bridge Loans and Private Corporate Bond Investments [Member]
Assets
Off-balance sheet commitments		0
Liabilities
Off-balance sheet commitments	$ 0

Total amount of mortgage loans not valued on a recurring basis as of the balance sheet date.

No definition available.

Name:	met_FairValueMortgageLoansNetNotOnRecurringBasis
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of mortgage loans held-for-investment.

+ References

No definition available.

+ Details

Name:	met_MortgagesHeldForInvestmentFairValueDisclosure
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of other investments not otherwise specified in the taxonomy.

+ References

No definition available.

+ Details

Name:	met_OtherInvestmentsFairValueDisclosure
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The fair value portion of investments in other limited partnership interests.

+ References

No definition available.

+ Details

Name:	met_OtherLimitedPartnershipInterestsFairValueDisclosure
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of the liability of policyholders for deposits held under the terms of insurance contracts.

+ References

No definition available.

+ Details

Name:	met_PolicyholderContractDepositsFairValueDisclosure
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

+ Details

Name:	us-gaap_DepositsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fair value of financial assets, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13433-108611

+ Details

Name:	us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The fair value of financial liabilities, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

+ Details

Name:	us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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

- Details

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

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Junior Subordinated Notes, which have a lower priority than senior instruments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16(a))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20, 22

-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 13, 16

-Article 9

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_JuniorSubordinatedNotes
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before allowance of loans made to policy and contract holders using their life insurance contracts' cash value or separate accounts as collateral. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums over and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

+ Details

Name:	us-gaap_LoansInsurancePolicy
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of mortgage loans held-for-sale.

+ References

No definition available.

+ Details

Name:	us-gaap_MortgagesHeldForSaleFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of other assets.

+ References

No definition available.

+ Details

Name:	us-gaap_OtherAssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of other liabilities.

+ References

No definition available.

+ Details

Name:	us-gaap_OtherLiabilitiesFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The book value of investments in real estate joint ventures including direct and indirect investments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(d))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_RealEstateInvestmentsJointVentures
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of receivables, including, but not limited to, trade account receivables, note receivables, and loan receivables.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3, 4

-Article 5

+ Details

Name:	us-gaap_ReceivablesFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_SecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of liability for variable contracts that meet specified criteria that are backed by assets held in separate accounts and carried at the fair value of those assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 80

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6484091&loc=d3e19268-158472

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-Glossary Separate Account

-URI http://asc.fasb.org/extlink&oid=6524887

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 80

-Section 50

-Paragraph 1

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 18

-Article 7

+ Details

Name:	us-gaap_SeparateAccountsLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant