INCOME TAXES - Significant Items in Net Deferred Tax Liability (Details) - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014
Deferred tax assets:
Reserves not currently deductible	$ 14.8	$ 16.0
Pension and other postretirement benefits	62.5	67.3
Operating losses	47.3	8.0
Unamortized investment tax credits	1.5	1.6
Other	0.0	28.9
Total deferred tax assets	126.1	121.8
Deferred tax liabilities:
Relating to property	472.1	366.9
Regulatory pension and other postretirement benefits	110.6	108.5
Deferred gas costs	8.1	20.4
Other	11.6	19.7
Total deferred tax liabilities	602.4	515.5
Net deferred tax asset (liability)	(476.3)	(393.7)
Net deferred tax asset (liability) – current	5.8	(9.9)
Det deferred tax asset (liability) - noncurrent	(482.1)	(383.8)
Laclede Gas
Deferred tax assets:
Reserves not currently deductible	15.4	16.0
Pension and other postretirement benefits	62.5	67.3
Operating losses	3.7	2.9
Unamortized investment tax credits	1.5	1.6
Other	0.0	17.8
Total deferred tax assets	83.1	105.6
Deferred tax liabilities:
Relating to property	425.0	361.2
Regulatory pension and other postretirement benefits	120.2	119.2
Deferred gas costs	8.2	20.4
Other	14.5	15.9
Total deferred tax liabilities	567.9	516.7
Net deferred tax asset (liability)	(484.8)	(411.1)
Net deferred tax asset (liability) – current	0.4	(11.3)
Det deferred tax asset (liability) - noncurrent	(485.2)	(399.8)
Alagasco
Deferred tax assets:
Reserves not currently deductible	7.0	2.5
Pension and other postretirement benefits	9.6	10.6
Goodwill	251.5	266.1
Operating losses	32.4	5.1
Other	1.4	0.2
Total deferred tax assets	301.9	284.5
Deferred tax liabilities:
Relating to property	45.1	4.0
Other	2.2	0.4
Total deferred tax liabilities	47.3	4.4
Net deferred tax asset (liability)	254.6	280.1
Net deferred tax asset (liability) – current	6.2	2.3
Det deferred tax asset (liability) - noncurrent	$ 248.4	$ 277.8