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PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS - Changes in Plan Assets and Benefit Obligations (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Sep. 30, 2014 | Sep. 30, 2013 | Sep. 30, 2012
Pension Plans |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Current year actuarial (gain) loss | $ 15.7 | [1] | $ 17.0 | $ 32.9
Amortization of actuarial loss | (7.1) | [1] | (10.7) | (29.1)
Acceleration of loss recognized due to settlement | (1.5) | [1] | (27.0) | 0
Amortization of prior service cost | (0.5) | [1] | (0.5) | (0.6)
Sub-total | 6.6 | [1] | (21.2) | 3.2
Regulatory adjustment | (6.1) | [1] | 21.1 | (3.5)
Total recognized in other comprehensive income | 0.5 | [1] | (0.1) | (0.3)
Postretirement Plans |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Current year actuarial (gain) loss | (3.1) | [1] | 16.3 | 10.1
Amortization of actuarial loss | (6.0) | [1] | (5.3) | (4.3)
Amortization of prior service cost | 2.5 | [1] | 0 | 2.1
Amortization of transition obligation | 0 | [1] | (0.1) | (0.1)
Sub-total | (6.6) | [1] | 10.9 | 7.8
Regulatory adjustment | 6.6 | [1] | (10.9) | (7.8)
Total recognized in other comprehensive income | 0 | [1] | 0 | 0
Laclede Gas | Pension Plans |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Current year actuarial (gain) loss | 14.2 |  | 17.0 | 32.9
Amortization of actuarial loss | (7.1) |  | (10.7) | (29.1)
Acceleration of loss recognized due to settlement | (1.5) |  | (27.0) | 0
Amortization of prior service cost | (0.5) |  | (0.5) | (0.6)
Sub-total | 5.1 |  | (21.2) | 3.2
Regulatory adjustment | (4.7) |  | 21.1 | (3.5)
Total recognized in other comprehensive income | 0.4 |  | (0.1) | (0.3)
Laclede Gas | Postretirement Plans |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Current year actuarial (gain) loss | (4.2) |  | 16.3 | 10.1
Amortization of actuarial loss | (6.0) |  | (5.3) | (4.3)
Amortization of prior service cost | 2.5 |  | 0 | 2.1
Amortization of transition obligation | 0 |  | (0.1) | (0.1)
Sub-total | (7.7) |  | 10.9 | 7.8
Regulatory adjustment | 7.7 |  | (10.9) | (7.8)
Total recognized in other comprehensive income | $ 0 |  | $ 0 | $ 0
[1] | Includes Alagasco.

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- Definition Before tax amount of the (increase) decrease in the value of the projected benefit obligation and the increase (decrease) in the value of the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption that has not been recognized in net periodic benefit cost. + References No definition available. + Details
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- Definition The difference between the period's net benefit cost recognized in other comprehensive income for defined benefit plans calculated in accordance with GAAP and the amount of recovery allowed in rates by the Missouri Public Service Commission. These differences are deferred as regulatory assets or regulatory liabilities. + References No definition available. + Details
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- Definition Before tax amount of the income statement impact of the reclassification adjustment for actuarial gain (loss) recognized as a component of net periodic benefit cost. + References No definition available. + Details
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- Definition The aggregate net gain (loss) recognized in other comprehensive income, net of any regulatory adjustments, including amounts arising during the period and reclassification adjustments of other comprehensive income as a result of being recognized as components of net periodic benefit cost for the period. + References No definition available. + Details
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- Definition Amount before tax, after reclassification adjustments, of actuarial gain (loss) that has not been recognized in the income statement. + 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 (i) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=28358780&loc=SL7669646-108580 + Details
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- Definition Amount before tax, after reclassification adjustments, of prior service cost (credit) that has not been recognized in the income statement. + 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 (i) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=28358780&loc=SL7669646-108580 + Details
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- Definition Amount before tax of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) related to pension and other postretirement benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=28358780&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=28358780&loc=SL7669646-108580 + Details
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- Definition Amount before tax of reclassification adjustment from accumulated other comprehensive income (loss) for net transition asset (obligation) related to pension and other postretirement benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=28358780&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=28358780&loc=d3e689-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 + Details
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