The number of manufactured gas plant (MGP) sites in Missouri posing potential environmental liability at St Louis.

No definition available.

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

- Definition

The number of former manufactured gas plant (MGP) sites in Missouri posing potential environmental liability.

+ References

No definition available.

+ Details

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

- Definition

The number of manufactured gas plant (MGP) sites in Missouri posing potential environmental liability at Shrewsbury.

+ References

No definition available.

+ Details

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

- Definition

Site Contingency, Number of Former Manufactured Gas Distribution

+ References

No definition available.

+ Details

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

- Definition

Site Contingency, Number of Former Manufactured Gas Plant

+ References

No definition available.

+ Details

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

- Definition

Site Contingency, Number of Residents Contaminated

+ References

No definition available.

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

The estimated maximum amount of possible loss from the contingency.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

+ Details

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

- Definition

The estimated minimum amount of possible loss from the contingency.

+ References

+ Details

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

- Details

Name:	dei_LegalEntityAxis=lg_AlabamaGasCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=lg_PreviousOwnershipMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=lg_MissouriGasEnergyMgeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=lg_LacledeGasCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=lg_CurrentOwnershipMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationContingencyAxis=lg_RemovalActionPhaseIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=lg_A35thAvenueSuperfundSiteMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationContingencyAxis=lg_RemovalActionPhaseIIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

COMMITMENTS AND CONTINGENCIES - Contingencies (Details) $ in Millions	Jun. 30, 2015 site	Aug. 30, 2014 USD ($) site Resident	Sep. 30, 2013 Resident
Loss Contingencies [Line Items]
Number of former manufactured gas plant (MGP) sites in Missouri	3
Number of former manufactured gas plant (MGP) sites in Shrewsbury, Missouri	1
Number of former manufactured gas plant (MGP) sites in the City of St. Louis	2
Minimum cost estimate for a one-time contractual transfer of risk \| $		$ 8.1
Maximum cost estimate for a one-time contractual transfer of risk \| $		$ 39.3
Alagasco
Loss Contingencies [Line Items]
Number of former manufactured gas plant (MGP)	9
Number of former manufactured gas distribution	5
Previous Ownership \| Missouri Gas Energy (MGE)
Loss Contingencies [Line Items]
Number of former manufactured gas plant (MGP)	7
Previous Ownership \| Laclede Gas
Loss Contingencies [Line Items]
Number of former manufactured gas plant (MGP)		19
Current Ownership \| Alagasco
Loss Contingencies [Line Items]
Number of former manufactured gas plant (MGP)	4
Number of former manufactured gas distribution	1
Removal Action, Phase I \| 35th Avenue Superfund Site
Loss Contingencies [Line Items]
Number of residents at high levels of contamination \| Resident			50
Removal Action, Phase II \| 35th Avenue Superfund Site
Loss Contingencies [Line Items]
Number of residents at high levels of contamination \| Resident		30