PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS - Pre-tax Amortization from AOCI (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014
Pension Plans
Pre-tax amounts are expected to be amortized from accumulated other comprehensive income [Abstract]
Amortization of net actuarial loss	$ 122.9
Amortization of prior service cost	4.0
Sub-total	126.9
Regulatory adjustment	(122.3)
Total	4.6
Postretirement Plans
Pre-tax amounts are expected to be amortized from accumulated other comprehensive income [Abstract]
Amortization of net actuarial loss	5.1	[1]
Amortization of prior service cost	0.8	[1]
Sub-total	5.9	[1]
Regulatory adjustment	(5.9)	[1]
Total	0	[1]
Laclede Gas | Pension Plans
Pre-tax amounts are expected to be amortized from accumulated other comprehensive income [Abstract]
Amortization of net actuarial loss	121.4
Amortization of prior service cost	4.0
Sub-total	125.4
Regulatory adjustment	(122.3)
Total	3.1
Laclede Gas | Postretirement Plans
Pre-tax amounts are expected to be amortized from accumulated other comprehensive income [Abstract]
Amortization of net actuarial loss	5.1
Amortization of prior service cost	0.8
Sub-total	5.9
Regulatory adjustment	(5.9)
Total	$ 0

[1] Includes Alagasco.