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Pension Plans and Other Postretirement Benefits - Pre-tax Amounts Recognized in Accumulated Other Comprehensive Loss Not Yet Recognized as Components of Net Periodic Pension Costs (Details) - USD ($) $ in Millions | Sep. 30, 2020 | Sep. 30, 2019
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Pension Plans |  |
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of: |  |
Net actuarial loss | $ 235.6 | $ 213.7
Prior service (credit) cost | (25.6) | (23.7)
Subtotal | 210.0 | 190.0
Adjustments for amounts included in regulatory assets | (206.7) | (187.1)
Total | 3.3 | 2.9
Other Postretirement Plans |  |
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of: |  |
Net actuarial loss | (61.7) | (56.3)
Prior service (credit) cost | 15.5 | (1.0)
Subtotal | (46.2) | (57.3)
Adjustments for amounts included in regulatory assets | 46.2 | 57.3
Spire Missouri | Pension Plans |  |
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of: |  |
Net actuarial loss | 152.9 | 153.1
Prior service (credit) cost | (2.8) | 1.7
Subtotal | 150.1 | 154.8
Adjustments for amounts included in regulatory assets | (146.8) | (151.9)
Total | 3.3 | 2.9
Spire Missouri | Other Postretirement Plans |  |
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of: |  |
Net actuarial loss | (58.3) | (52.6)
Prior service (credit) cost | 10.4 | 0.6
Subtotal | (47.9) | (52.0)
Adjustments for amounts included in regulatory assets | 47.9 | 52.0
Spire Alabama | Pension Plans |  |
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of: |  |
Net actuarial loss | 78.1 | 61.9
Prior service (credit) cost | (21.1) | (23.5)
Subtotal | 57.0 | 38.4
Adjustments for amounts included in regulatory assets | (57.0) | (38.4)
Total | 0.0 | 0.0
Spire Alabama | Other Postretirement Plans |  |
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of: |  |
Net actuarial loss | (1.5) | (2.6)
Prior service (credit) cost | 5.1 | (1.6)
Subtotal | 3.6 | (4.2)
Adjustments for amounts included in regulatory assets | $ (3.6) | $ 4.2

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- Definition The pretax total, net of regulatory adjustments, of net gain (loss), prior service cost (credit), and transition assets (obligations), included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost net of adjustments for amounts included in regulatory assets. + References No definition available. + Details
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- Definition Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669646-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580 + Details
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- Definition Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580 + Details
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