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Income Taxes - Impact of Tax Cuts and Jobs Act (Details) $ in Millions | 12 Months Ended
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Sep. 30, 2018 USD ($)
Spire |
Deferred Income Tax Assets And Liabilities [Line Items] |
Adjustment to deferred tax liabilities | $ (318.3)
Adjustment to deferred income tax expense | (75.0)
Adjustment to regulatory assets | (75.9)
Adjustment to regulatory liabilities | 167.4
Spire Missouri |
Deferred Income Tax Assets And Liabilities [Line Items] |
Adjustment to deferred tax liabilities | (285.3)
Adjustment to deferred income tax expense | (57.0)
Adjustment to regulatory assets | (78.1)
Adjustment to regulatory liabilities | 150.2
Spire Alabama |
Deferred Income Tax Assets And Liabilities [Line Items] |
Adjustment to deferred tax liabilities | (61.0)
Adjustment to deferred income tax expense | 58.8
Adjustment to regulatory assets | $ 2.2

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