Anticipated contributions to the pension plans for fiscal year 2012 for non-qualified plans.

No definition available.

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- Definition

Anticipated contributions to the pension plans for the next fiscal year for qualified trusts.

+ References

No definition available.

+ Details

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- Definition

Anticipated contribution to the postretirement plans for the next fiscal year for qualified trusts.

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

Defined Benefit Plan, Lump-sum Payment Recognized as Settlement Gain (Loss), Minimum Threshold

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

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.

+ References

No definition available.

+ Details

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- Definition

-- None. No documentation exists for this element. --

+ References

No definition available.

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- Definition

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.

+ References

No definition available.

+ Details

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- Definition

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.

+ References

No definition available.

+ Details

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- Definition

Amount of (increase) decrease to benefit obligation of defined benefit plan from remeasurement due to settlement. Excludes decrease to benefit obligation for settlement payment.

+ 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 (a)(10)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one 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 (d)(5)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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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 cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Jan. 01, 2011	Feb. 20, 2010
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Extent of Lump-sum payments recognized, percentage	100.00%
Implementation period used to calculate return on plan assets	4 years
Gains or losses includible in cost amortized to extent exceeds benefit obligations or market-related value of plan assets, percentage	10.00%
Anticipated Contributions to pension plans for qualified trust	$ 35.5
Anticipated contributions to pension plans for non-qualified plans	$ 0.5
Medical insurance available until age is reached after early retirement	65 years
Recovery in rates for postretirement benefit				$ 9.5
Spire Missouri
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Recovery in rates for the qualified pension plans base allowance				$ 15.5
Other Plans [Abstract]
401(K) plans, cost of defined contributions	$ 8.4	$ 8.2	$ 8.0
Spire Alabama
Other Plans [Abstract]
401(K) plans, cost of defined contributions	2.7	2.3	3.0
Spire Missouri West
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Recovery in rates for the qualified pension plans base allowance					$ 10.0
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Settlement benefits paid	$ 62.2	$ 16.6	71.1
Pension Plans \| Spire Missouri
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Targeted allocation of plan assets	100.00%	100.00%
Settlement benefits paid	$ 43.5	$ 0.0	58.2
Pension Plans \| Spire Alabama
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Targeted allocation of plan assets	100.00%	100.00%
Settlement benefits paid	$ 18.7	$ 16.6	$ 12.9
Postretirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Anticipated contributions to the postretirement plans for qualified trusts	7.2
Anticipated payment directly to participants in postretirement plan	$ 0.2
Postretirement Plans \| Spire Missouri
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Targeted allocation of plan assets	100.00%
Postretirement Plans \| Spire Alabama
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Targeted allocation of plan assets	100.00%
Equity markets \| Pension Plans \| Spire Missouri
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Targeted allocation of plan assets	56.40%	56.20%
Equity markets \| Pension Plans \| Spire Alabama
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Targeted allocation of plan assets	60.00%	60.00%
Equity markets \| Postretirement Plans \| Spire Missouri
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Targeted allocation of plan assets	60.00%
Equity markets \| Postretirement Plans \| Spire Alabama
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Targeted allocation of plan assets	60.00%
Debt securities \| Pension Plans \| Spire Missouri
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Targeted allocation of plan assets	43.60%	43.80%
Debt securities \| Postretirement Plans \| Spire Missouri
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Targeted allocation of plan assets	40.00%
Debt securities \| Postretirement Plans \| Spire Alabama
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Targeted allocation of plan assets	40.00%