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REGULATORY MATTERS - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions | Sep. 30, 2017 | Sep. 30, 2016
--- | --- | ---
Regulatory Assets [Line Items] |  |
Regulatory assets, current | $ 175.5 | $ 93.9
Regulatory assets, non current | 791.1 | 838.0
Total Regulatory Assets | 966.6 | 931.9
Pension and postretirement benefit costs |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, current | 42.2 | 27.0
Regulatory assets, non current | 404.7 | 487.9
Unamortized purchased gas adjustments |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, current | 102.6 | 49.7
Future income taxes due from customers |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, non current | 170.5 | 151.3
Accrued cost of removal |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, non current | 123.3 | 130.6
Unamortized purchased gas adjustments |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, non current | 9.9 | 12.6
Energy efficiency |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, non current | 29.0 | 25.5
Other |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, current | 30.7 | 17.2
Regulatory assets, non current | 53.7 | 30.1
Spire Missouri |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, current | 95.6 | 67.0
Regulatory assets, non current | 557.8 | 589.8
Total Regulatory Assets | 653.4 | 656.8
Spire Missouri | Pension and postretirement benefit costs |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, current | 34.9 | 20.2
Regulatory assets, non current | 322.7 | 375.7
Spire Missouri | Unamortized purchased gas adjustments |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, current | 57.4 | 43.1
Spire Missouri | Future income taxes due from customers |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, non current | 170.5 | 151.3
Spire Missouri | Accrued cost of removal |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, non current | 0.0 | 0.0
Spire Missouri | Unamortized purchased gas adjustments |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, non current | 9.9 | 12.6
Spire Missouri | Energy efficiency |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, non current | 29.0 | 25.5
Spire Missouri | Other |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, current | 3.3 | 3.7
Regulatory assets, non current | 25.7 | 24.7
Spire Alabama |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, current | 64.6 | 20.5
Regulatory assets, non current | 197.0 | 230.7
Total Regulatory Assets | 261.6 | 251.2
Spire Alabama | Pension and postretirement benefit costs |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, current | 7.2 | 6.8
Regulatory assets, non current | 72.6 | 98.9
Spire Alabama | Unamortized purchased gas adjustments |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, current | 45.2 | 5.6
Spire Alabama | Future income taxes due from customers |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, non current | 0.0 | 0.0
Spire Alabama | Accrued cost of removal |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, non current | 123.3 | 130.6
Spire Alabama | Unamortized purchased gas adjustments |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, non current | 0.0 | 0.0
Spire Alabama | Energy efficiency |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, non current | 0.0 | 0.0
Spire Alabama | Other |  |
Regulatory Assets [Line Items] |  |
Regulatory assets, current | 12.2 | 8.1
Regulatory assets, non current | $ 1.1 | $ 1.2

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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + 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 + Details
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