Amortization Of Regulatory Assets For Which No Return On Investment During Recovery Period Is Provided

No definition available.

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- Definition

Percentage of savings due to cost management program allowed to be retained by the entity.

+ References

No definition available.

+ Details

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- Definition

The revenue of off system sales attributable to customers.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Maximum amount of annual cost savings that the utility is able to retain under cost savings plan.

+ References

No definition available.

+ Details

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- Definition

Minimum number of months that is required between discretionary PGA changes.

+ References

No definition available.

+ Details

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- Definition

Number of discretionary PGA changes the Utility can make during each fiscal year.

+ References

No definition available.

+ Details

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- Definition

Public Utilities, Approved Rate Increase (Decrease), Annualized Revenue

+ References

No definition available.

+ Details

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- Definition

Public Utilities, Approved Rate Increase (Decrease), Impact To Earnings Per Share

+ References

No definition available.

+ Details

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- Definition

Public Utilities, Approved Rate Increase (Decrease), Impact To Net Income (Loss)

+ References

No definition available.

+ Details

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- Definition

Public Utilities, Approved Rate Increase (Decrease), Incentive Compensation Costs Excluded From Rate Base

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Public Utilities, Approved Rate Increase (Decrease), Incentive Compensation Costs From Buildings Sold Excluded From Rate Base

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Public Utilities, Approved Rate Increase (Decrease), Rate Case Expenses Excluded From Rate Base

+ References

No definition available.

+ Details

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Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Public Utilities, Approved Rate Increase (Decrease), Regulatory Costs

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Public Utilities, Recommended Rate Increase (Decrease), Amount

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount authorized by State regulatory for the issuance of debt securities, preferred stock, capital leases, and to issue common stock and receive paid-in capital which remains available to issue at period end

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)

+ References

No definition available.

+ Details

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- Definition

The increase (decrease) during the reporting period in the value of other assets that are created when regulatory agencies permits public utilities to defer costs to the balance sheet.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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- Definition

Amount of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

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- 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

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- Definition

Amount of public utility's requested rate increase (decrease) with regulatory agency.

+ References

No definition available.

+ Details

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- Definition

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Remaining recovery period of regulatory assets for which no return on investment during recovery period is provided, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 55
-Paragraph 2
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-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

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REGULATORY MATTERS - Spire Missouri (Details)						9 Months Ended	12 Months Ended
REGULATORY MATTERS - Spire Missouri (Details)	Sep. 28, 2018 USD ($)	Jun. 07, 2018 USD ($)	Mar. 07, 2018 USD ($) $ / shares	Sep. 15, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2018 USD ($)	Sep. 30, 2018 USD ($) operating_segment	Sep. 20, 2018 USD ($)	Apr. 19, 2018 USD ($)	Sep. 30, 2017 USD ($)	Apr. 11, 2017 USD ($)
Public Utilities, General Disclosures [Line Items]
Customer Share					100.00%		75.00%			85.00%
Decreases resulting from TCJA's federal rate reduction			$ 33,000,000
Regulatory assets							$ 742,600,000			$ 966,600,000
Remaining recovery period for regulatory assets for which no return on investment during recovery period is provided							15 years
Regulatory costs							$ 30,600,000
Spire Missouri
Public Utilities, General Disclosures [Line Items]
Number of PGA Discretionary Changes \| operating_segment							3
Months between PGA Discretionary Changes							2 months
Regulatory assets							$ 471,800,000			$ 653,400,000
Regulatory preferred stock and debt securities issuance, amount authorized							$ 500,000,000
Spire Missouri East
Public Utilities, General Disclosures [Line Items]
Customer Share							25.00%
Spire Missouri West
Public Utilities, General Disclosures [Line Items]
Customer Share							25.00%
MoPSC
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), annualized revenue				$ 200,000
MoPSC \| Spire Missouri
Public Utilities, General Disclosures [Line Items]
Cost savings retention percentage							10.00%
Maximum amount of cost savings allowable							$ 3.0
Regulatory preferred stock and debt securities issuance, amount authorized								$ 500,000,000
MoPSC \| Spire Missouri East
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) amount			18,000,000
MoPSC \| Spire Missouri West
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) amount			15,200,000
Infrastructure System Replacement Surcharge
Public Utilities, General Disclosures [Line Items]
Recommended rate increase (decrease) amount					$ 3,000,000
Infrastructure System Replacement Surcharge \| Spire Missouri East
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) amount	$ 2,600,000
Approved rate increase (decrease), annualized revenue					4,500,000
Requested rate increase		$ 4,800,000
Infrastructure System Replacement Surcharge \| Spire Missouri West
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) amount	$ 5,400,000
Approved rate increase (decrease), annualized revenue					$ 3,200,000
Requested rate increase		$ 7,100,000
Infrastructure System Replacement Surcharge \| MoPSC
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) amount			0
Incentive compensation costs			6,900,000
Incentive compensation costs, assets			1,800,000
Rate case expenses			900,000
Regulatory costs							$ 38,400,000
After-tax rate reduction to net income			$ 23,600,000
After-tax rate reduction to earnings per share \| $ / shares			$ 0.49
Infrastructure System Replacement Surcharge \| MoPSC \| Spire Missouri East
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) amount			$ 32,600,000
Approved rate increase (decrease), annualized revenue			14,600,000
Infrastructure System Replacement Surcharge \| MoPSC \| Spire Missouri West
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) amount			16,400,000
Approved rate increase (decrease), annualized revenue			1,200,000
Pension Cost \| Infrastructure System Replacement Surcharge \| MoPSC
Public Utilities, General Disclosures [Line Items]
Regulatory assets recovery			(28,800,000)
Regulatory costs			30,600,000
Pension Cost \| Infrastructure System Replacement Surcharge \| MoPSC \| Spire Missouri East
Public Utilities, General Disclosures [Line Items]
Regulatory assets			29,000,000								$ 15,500,000
Pension Cost \| Infrastructure System Replacement Surcharge \| MoPSC \| Spire Missouri West
Public Utilities, General Disclosures [Line Items]
Regulatory assets			5,500,000								9,900,000
Postretirement Benefit Costs \| Infrastructure System Replacement Surcharge \| MoPSC \| Spire Missouri East
Public Utilities, General Disclosures [Line Items]
Regulatory assets			$ 8,600,000						$ 8,600,000		$ 9,500,000
Pension and Other Postretirement Benefits \| Spire Missouri East
Public Utilities, General Disclosures [Line Items]
Remaining recovery period for regulatory assets for which no return on investment during recovery period is provided						8 years	8 years
Amortization of assets						$ 173,000,000	$ 173,000,000
Pension and Other Postretirement Benefits \| Spire Missouri West
Public Utilities, General Disclosures [Line Items]
Amortization of assets						$ 26,200,000	$ 26,200,000