XML 55 R41.htm IDEA: XBRL DOCUMENT
v3.8.0.1

PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS - Net Periodic Cost (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Pension Plans |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service cost – benefits earned during the period | $ 5.2 | $ 5.3
Interest cost on projected benefit obligation | 6.9 | 6.9
Expected return on plan assets | (9.7) | (9.9)
Amortization of prior service credit | (0.3) | 0.2
Amortization of actuarial gain (loss) | 3.1 | 3.4
Subtotal | 5.2 | 5.9
Regulatory adjustment | 4.3 | 4.6
Net pension cost (income) | 9.5 | 10.5
Postretirement Plans |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service cost – benefits earned during the period | 2.3 | 2.8
Interest cost on projected benefit obligation | 2.2 | 2.1
Expected return on plan assets | (3.5) | (3.4)
Amortization of actuarial gain (loss) | 0.2 | 0.6
Subtotal | 1.2 | 2.1
Regulatory adjustment | 0.1 | (0.8)
Net pension cost (income) | 1.3 | 1.3
Spire Missouri | Pension Plans |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service cost – benefits earned during the period | 3.3 | 3.3
Interest cost on projected benefit obligation | 4.9 | 4.8
Expected return on plan assets | (7.2) | (7.3)
Amortization of prior service credit | 0.2 | 0.2
Amortization of actuarial gain (loss) | 2.6 | 2.9
Subtotal | 3.8 | 3.9
Regulatory adjustment | 2.4 | 2.8
Net pension cost (income) | 6.2 | 6.7
Spire Missouri | Postretirement Plans |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service cost – benefits earned during the period | 2.2 | 2.6
Interest cost on projected benefit obligation | 1.8 | 1.7
Expected return on plan assets | (2.4) | (2.3)
Amortization of prior service credit | 0.1 | 0.1
Amortization of actuarial gain (loss) | 0.2 | 0.6
Subtotal | 1.9 | 2.7
Regulatory adjustment | 0.5 | (0.4)
Net pension cost (income) | 2.4 | 2.3
Spire Alabama | Pension Plans |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service cost – benefits earned during the period | 1.6 | 1.6
Interest cost on projected benefit obligation | 1.4 | 1.5
Expected return on plan assets | (1.7) | (1.8)
Amortization of prior service credit | (0.5) | 0.0
Amortization of actuarial gain (loss) | 0.5 | 0.5
Subtotal | 1.3 | 1.8
Regulatory adjustment | 1.7 | 1.6
Net pension cost (income) | 3.0 | 3.4
Spire Alabama | Postretirement Plans |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service cost – benefits earned during the period | 0.0 | 0.1
Interest cost on projected benefit obligation | 0.4 | 0.4
Expected return on plan assets | (1.0) | (1.1)
Amortization of prior service credit | (0.1) | (0.1)
Subtotal | (0.7) | (0.7)
Regulatory adjustment | (0.4) | (0.4)
Net pension cost (income) | $ (1.1) | $ (1.1)

X
- Definition The difference between the period's net benefit cost recognized in other comprehensive income for defined benefit plans calculated in accordance with GAAP and the amount of recovery allowed in rates by the Missouri Public Service Commission. These differences are deferred as regulatory assets or regulatory liabilities. + References No definition available. + Details
Name: | lg_DefinedBenefitPlanIncreaseDecreaseRegulatoryAdjustment
Namespace Prefix: | lg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The total amount of periodic benefit cost for defined benefit plans for the period after the impact of regulatory adjustment. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain or loss, prior service cost or credit, transition asset or obligation, and gain or loss due to settlements or curtailments. + References No definition available. + Details
Name: | lg_DefinedBenefitPlanNetPeriodicBenefitCostAfterRegulatoryAdjustment
Namespace Prefix: | lg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(5) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of cost recognized for passage of time related to defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanInterestCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of net periodic benefit cost (credit) for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanServiceCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
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: |

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