Name:	lg_AnticipatedContributionsToOtherPostretirementBenefitPlansQualifiedTrusts
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

Anticipated contributions to pension plan for the remaining fiscal year for qualified trusts.

No definition available.

Name:	lg_AnticipatedContributionsToPensionPlanQualifiedTrusts
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

Anticipated contributions to the pension plans for the remaining fiscal year for non-qualified trusts.

No definition available.

Name:	lg_AnticipatedContributionsToPensionPlansNonQualifiedTrust
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

Anticipated payment to the postretirement plans participants for the remaining fiscal year for non-qualified trusts.

No definition available.

Name:	lg_AnticipatedPaymentDirectlyToParticipantsInOtherPostretirementPlan
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

The amount of contributions made to the pension plans for non-qualified plans by the employer for the current fiscal year, through the current period.

No definition available.

Name:	lg_ContributionsToPensionPlansForNonQualifiedPlans
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The amount of contributions made to the pension plans for qualified trusts by the employer for the current fiscal year, through the current period.

No definition available.

Name:	lg_ContributionsToPensionPlansForQualifiedTrust
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The amount of contributions to the postretirement plans paid directly to participants.

No definition available.

Name:	lg_ContributionsToPostretirementPlansForNonQualifiedTrusts
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Reflects the upper limit on age eligibility, post early retirement, when medical insurance is available to retiree.

No definition available.

Name:	lg_DefinedBenefitPlanMedicalInsuranceOfferedPostEarlyRetirementUntilAgeMaximum
Namespace Prefix:	lg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

The amount of contributions made to the postretirement plans for qualified trusts by the employer for the current fiscal year, through the current period.

No definition available.

Name:	lg_DefinedBenefitPlanOtherPostretirementBenefitPlansQualifiedTrustsContributionsByEmployerFiscalYearToDate
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Gains and losses not yet includible in pension/postretirement benefit cost are amortized only to the extent that such gain or loss exceeds 10% of the greater of the benefit obligation or the market-related value of plan assets.

No definition available.

Name:	lg_GainsOrLossesIncludibleInCostAmortizedToExtentExceedsProjectedBenefitObligationsOrMarketRelatedValueOfPlanAssetsPercentage
Namespace Prefix:	lg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Disclosure under Missouri Public Service Commission Order, the return on plan assets if based on the market-related value of plan assets implemented prospectively over a four-year period.

No definition available.

Name:	lg_ImplementationPeriodUsedToCalculateReturnOnPlanAssets
Namespace Prefix:	lg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Lump-sum payments recognized as settlements

No definition available.

Name:	lg_LumpSumPaymentsRecognizedAsSettlements
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The amortization period for transition obligation not yet in postretirement benefit costs.

No definition available.

Name:	lg_PostretirementBenefitCostAmortizationPeriod
Namespace Prefix:	lg_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

The amount of annual recovery of net pension costs allowed in rates for qualified pension plans by the Missouri Public Service Commission. The differences between these amounts and those calculated pursuant to GAAP are deferred as regulatory assets or liabilities.

No definition available.

Name:	lg_RateRecoveryOfBenefitCosts
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of annual recovery of postretirement benefit costs allowed in rates by the Missouri Public Service Commission. The differences between these amounts and those calculated pursuant to GAAP are deferred as regulatory assets or liabilities.

No definition available.

Name:	lg_ReoveryInRatesForPostretirmentBenefitPlansBaseAllowance
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

A description of the events that resulted in the settlement or curtailment of the employer's defined benefit plans.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (r)

-URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph r

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.