XML 124 R99.htm IDEA: XBRL DOCUMENT
v3.8.0.1

REGULATORY MATTERS - Schedule of Regulatory Assets Not Earnings a Return (Details) - USD ($) $ in Millions | Sep. 30, 2017 | Sep. 30, 2016
--- | --- | ---
Regulatory Assets [Line Items] |  |
Total Regulatory Assets Not Earning a Return | $ 380.3 | $ 404.8
Future income taxes due from customers |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets Not Earning a Return | 170.5 | 151.3
Pension and postretirement benefit costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets Not Earning a Return | 198.5 | 240.6
Other |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets Not Earning a Return | 11.3 | 12.9
Spire Missouri |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets Not Earning a Return | 380.3 | 404.8
Spire Missouri | Future income taxes due from customers |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets Not Earning a Return | 170.5 | 151.3
Spire Missouri | Pension and postretirement benefit costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets Not Earning a Return | 198.5 | 240.6
Spire Missouri | Other |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets Not Earning a Return | $ 11.3 | $ 12.9

X
- 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_RegulatoryAssetLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Remaining balance of regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 55 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82849221&loc=d3e44360-110383 + Details
Name: | us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_RegulatoryAssetAxis=us-gaap_DeferredIncomeTaxChargesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryAssetAxis=lg_PensionandPostretirementBenefitCostsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryAssetAxis=us-gaap_OtherRegulatoryAssetsLiabilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lg_SpireMissouriMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |