PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS - Amounts Recognized in Consolidated Balance Sheets (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Non-current liabilities	$ (244.9)		$ (228.6)
Pension Plans
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Current liabilities	(0.5)	[1]	(0.4)
Non-current liabilities	(185.4)	[1]	(158.0)
Total	(185.9)	[1]	(158.4)
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of:
Net actuarial loss	7.7	[1]	115.8
Prior service costs	0.5	[1]	4.5
Sub-total	8.2	[1]	120.3
Adjustments for amounts included in Regulatory Assets	(7.9)	[1]	(116.7)
Total	0.3	[1]	3.6
Postretirement Plans
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Non-current assets	25.0	[1]	2.5
Current liabilities	(0.3)	[1]	(0.3)
Non-current liabilities	(60.7)	[1]	(70.7)
Total	(36.0)	[1]	(68.5)
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of:
Net actuarial loss	54.4	[1]	63.6
Prior service costs	2.5	[1]	0
Transition obligation	0	[1]	0
Sub-total	56.9	[1]	63.6
Adjustments for amounts included in Regulatory Assets	(56.9)	[1]	(63.6)
Total	0	[1]	0
Laclede Gas
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Non-current liabilities	(215.3)		(228.7)
Laclede Gas | Pension Plans
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Current liabilities	(0.5)		(0.4)
Non-current liabilities	(155.7)		(158.0)
Total	(156.2)		(158.4)
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of:
Net actuarial loss	7.7		115.8
Prior service costs	0.5		4.5
Sub-total	8.2		120.3
Adjustments for amounts included in Regulatory Assets	(7.9)		(116.7)
Total	0.3		3.6
Laclede Gas | Postretirement Plans
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Non-current assets	0.3		2.5
Current liabilities	(0.3)		(0.3)
Non-current liabilities	(60.7)		(70.7)
Total	(60.7)		(68.5)
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of:
Net actuarial loss	53.3		63.6
Prior service costs	2.5		0
Transition obligation	0		0
Sub-total	55.8		63.6
Adjustments for amounts included in Regulatory Assets	(55.8)		(63.6)
Total	$ 0		$ 0

[1] Includes Alagasco.