INCOME TAXES - Significant Items in Net Deferred Tax Liability (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013
Deferred tax assets:
Reserves not currently deductible	$ 16.0		$ 13.9
Pension and other postretirement benefits	67.3		71.4
Unamortized investment tax credits	1.6		1.8
Other	36.9	[1]	12.5	[1]
Total deferred tax assets	121.8		99.6
Deferred tax liabilities:
Relating to property	366.9		342.0
Regulatory pension and other postretirement benefits	108.5		124.8
Deferred gas costs	20.4		7.1
Other	19.7		5.8
Total deferred tax liabilities	515.5		479.7
Total deferred tax liabilities	393.7		380.1
Net deferred tax liability - current	(9.9)	[1]	(1.0)	[1]
Net deferred tax liability - non-current	383.8	[1]	379.1	[1]
Laclede Gas
Deferred tax assets:
Reserves not currently deductible	16.0		13.9
Pension and other postretirement benefits	67.3		71.4
Unamortized investment tax credits	1.6		1.8
Other	20.7	[1]	10.5	[1]
Total deferred tax assets	105.6		97.6
Deferred tax liabilities:
Relating to property	361.2		342.0
Regulatory pension and other postretirement benefits	119.2		124.9
Deferred gas costs	20.4		7.1
Other	15.9		5.4
Total deferred tax liabilities	516.7		479.4
Total deferred tax liabilities	411.1		381.8
Net deferred tax liability - current	(11.3)	[1]	(1.7)	[1]
Net deferred tax liability - non-current	399.8	[1]	380.1	[1]
State
Deferred tax liabilities:
Tax credits included in net deferred tax liability	8.7
Tax credits classified as current	6.9
Tax credits classified as noncurrent	1.8
State | Laclede Gas
Deferred tax liabilities:
Tax credits included in net deferred tax liability	8.0
Tax credits classified as current	6.2
Tax credits classified as noncurrent	$ 1.8

[1] The Company periodically invests in tax credits. As of September 30, 2014, $8.7 of state tax credits are included in Other and Net deferred tax liability. $6.9 of state tax credits were classified as current. $1.8 of state tax credits were classified as non-current.