Reinsurance (Related Party Reinsurance Transactions - Narrative) (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reinsurance Disclosures [Abstract]
Net derivatives gains (losses)	$ (170,000,000)	$ 135,000,000	$ 598,000,000
Embedded Derivative, Fair Value of Embedded Derivative Asset	507,000,000	(168,000,000)
Other assets relating to variable interest entities	4,469,000,000us-gaap_OtherAssets	4,716,000,000us-gaap_OtherAssets
Other liabilities relating to variable interest entities	33,447,000,000us-gaap_OtherLiabilities	32,180,000,000us-gaap_OtherLiabilities
Future policy benefits	117,402,000,000	111,963,000,000
Premiums, reinsurance and other receivables	23,439,000,000us-gaap_PremiumsAndOtherReceivablesNet	23,637,000,000us-gaap_PremiumsAndOtherReceivablesNet
Deferred Policy Acquisition Costs and Value of Business Acquired	5,975,000,000	6,416,000,000	5,832,000,000
Other Policy-Related Balances	5,840,000,000mlic_OtherPolicyRelatedBalances	5,671,000,000mlic_OtherPolicyRelatedBalances
Other Income	1,808,000,000us-gaap_OtherIncome	1,699,000,000us-gaap_OtherIncome	1,730,000,000us-gaap_OtherIncome
Reinsurance Recoverables, Ceded	5,400,000,000mlic_ReinsuranceRecoverablesCeded	5,400,000,000mlic_ReinsuranceRecoverablesCeded
Deposit Contracts, Assets	13,800,000,000us-gaap_DepositContractsAssets	13,800,000,000us-gaap_DepositContractsAssets
Deposit Contracts, Liabilities	6,800,000,000us-gaap_DepositContractsLiabilities	6,500,000,000us-gaap_DepositContractsLiabilities
Ceded Credit Risk, Unsecured [Member]
Reinsurance Disclosures [Abstract]
Reinsurance Recoverables, Ceded	2,300,000,000	2,400,000,000
Affiliated Entity [Member]
Reinsurance Disclosures [Abstract]
Other Income	177,000,000	142,000,000	113,000,000
Deposit Contracts, Assets	11,700,000,000	11,800,000,000
Deposit Contracts, Liabilities	6,700,000,000	6,500,000,000
Affiliated Entity [Member] \| Ceded Credit Risk, Unsecured [Member]
Reinsurance Disclosures [Abstract]
Reinsurance Recoverables, Ceded	2,100,000,000	1,200,000,000
Affiliated Entity [Member] \| Closed Block Liabilities Ceded To MetLife Reinsurance Of Charleston [Member]
Reinsurance Disclosures [Abstract]
Embedded Derivative, Fair Value of Embedded Derivative Liability	1,100,000,000	709,000,000
Net derivatives gains (losses)	(389,000,000)	664,000,000	135,000,000
Affiliated Entity [Member] \| MLIC NY Separate Accts [Member]
Reinsurance Disclosures [Abstract]
Other assets relating to variable interest entities	192,000,000
Other liabilities relating to variable interest entities	572,000,000
Future policy benefits	128,000,000
Cash, Cash Equivalents, and Short-term Investments	494,000,000
Affiliated Entity [Member] \| Ceded Guaranteed Minimum Benefit [Member]
Reinsurance Disclosures [Abstract]
Net derivatives gains (losses)	497,000,000	(1,700,000,000)	14,000,000
Embedded Derivative, Fair Value of Embedded Derivative Asset	657,000,000	(62,000,000)
Affiliated Entity [Member] \| Funds Withheld On Ceded Reinsurance [Member]
Reinsurance Disclosures [Abstract]
Coinsurance Funds Withheld Basis, Percent	75.00%
Embedded Derivative, Fair Value of Embedded Derivative Liability	20,000,000	(11,000,000)
Net derivatives gains (losses)	(39,000,000)	40,000,000	(9,000,000)
Affiliated Entity [Member] \| Co-funds Withheld Exeter [Member]
Reinsurance Disclosures [Abstract]
Coinsurance Funds Withheld Basis, Percent	75.00%
Other liabilities relating to variable interest entities	432,000,000
Premiums, reinsurance and other receivables	492,000,000
Deferred Policy Acquisition Costs and Value of Business Acquired	30,000,000
Other Policy-Related Balances	9,000,000
Affiliated Entity [Member] \| Guarantee Minimum Benefits Exeter [Member]
Reinsurance Disclosures [Abstract]
Other liabilities relating to variable interest entities	447,000,000
Cash, Cash Equivalents, and Short-term Investments	324,000,000
Premiums, reinsurance and other receivables	719,000,000
Deferred Policy Acquisition Costs and Value of Business Acquired	7,000,000
Other Income	54,000,000
Affiliated Entity [Member] \| Variable Annuity FMLI [Member]
Reinsurance Disclosures [Abstract]
Other liabilities relating to variable interest entities	269,000,000
Cash, Cash Equivalents, and Short-term Investments	$ 218,000,000
Modco Variable Annuity Percentage	100.00%

Percentage of business ceded on a coinsurance funds withheld basis.

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Percentage of business ceded on a modified coinsurance basis.

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Liability as of the balance sheet date to the policyholders for funds held that are returnable under the terms of insurance contracts that were not separately reported. Also includes unearned premiums.

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Amount of reinsurance recoverable balances in both asset and liability accounts that have been ceded.

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Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

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Carrying (unamortized) amount as of the balance sheet date of deferred policy acquisition costs and value of business acquired (also called present value of future profits).

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Carrying amount of assets as of the balance sheet date pertaining to amounts paid by the insured (including a ceding company) under insurance or reinsurance contracts for which insurance risk is not transferred.

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Carrying amount of liabilities as of the balance sheet date pertaining to amounts received by the insurer or reinsurer from the insured (including a ceding company) under insurance or reinsurance contracts for which insurance risk is not transferred.

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Fair value as of the balance sheet date of the embedded derivative or group of embedded derivatives classified as an asset.

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Fair value as of the balance sheet date of the embedded derivative or group of embedded derivatives classified as a liability.

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Net Increase or Decrease in the fair value of the embedded derivative or group of embedded derivatives included in earnings in the period.

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Amount of accrued obligation to policyholders that relates to insured events for long-duration contracts.

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The aggregate carrying amounts, as of the balance sheet date, of assets not separately disclosed in the balance sheet.

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Reflects the sum of all other revenue and income recognized by the entity in the period not otherwise specified in the income statement.

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The aggregate carrying amount, as of the balance sheet date, of liabilities not separately disclosed in the balance sheet.

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Carrying amount as of the balance sheet date, net of allowance for doubtful accounts, of all premiums and other types of receivables due from other persons or entities.

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