PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS - Targeted and Actual Plan Assets by Category (Details)	12 Months Ended
	Sep. 30, 2014		Sep. 30, 2013
Alagasco | Pension Plans
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	100.00%
Actual allocation of plan assets	100.00%
Alagasco | Pension Plans | Equity Markets
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	46.00%
Actual allocation of plan assets	46.00%
Alagasco | Pension Plans | Commodities
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	33.00%
Actual allocation of plan assets	29.00%
Alagasco | Pension Plans | Real Estate
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	21.00%
Actual allocation of plan assets	25.00%
Alagasco | Postretirement Plans
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	100.00%
Actual allocation of plan assets	100.00%
Alagasco | Postretirement Plans | Equity Markets
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	60.00%
Actual allocation of plan assets	60.00%
Alagasco | Postretirement Plans | Debt Securities
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	40.00%
Actual allocation of plan assets	40.00%
Alagasco | Postretirement Plans | Other
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	0.00%
Actual allocation of plan assets	0.00%
Laclede Gas | Pension Plans
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	100.00%
Actual allocation of plan assets	100.00%		100.00%
Laclede Gas | Pension Plans | Equity Markets
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	45.50%
Actual allocation of plan assets	46.70%		45.90%
Laclede Gas | Pension Plans | Commodities
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	1.50%
Actual allocation of plan assets	1.50%		1.60%
Laclede Gas | Pension Plans | Real Estate
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	1.50%
Actual allocation of plan assets	1.50%		3.00%
Laclede Gas | Pension Plans | Inflation-Indexed Securities
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	1.50%
Actual allocation of plan assets	1.50%		1.40%
Laclede Gas | Pension Plans | Debt Securities
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	50.00%
Actual allocation of plan assets	48.70%		43.30%
Laclede Gas | Pension Plans | Other
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	0.00%	[1]
Actual allocation of plan assets	0.10%	[1]	4.80%	[1]
Laclede Gas | Postretirement Plans
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	100.00%
Actual allocation of plan assets	100.00%		100.00%
Laclede Gas | Postretirement Plans | Equity Markets
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	60.00%
Actual allocation of plan assets	59.00%		59.00%
Laclede Gas | Postretirement Plans | Debt Securities
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	40.00%
Actual allocation of plan assets	39.00%		39.00%
Laclede Gas | Postretirement Plans | Other
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	0.00%
Actual allocation of plan assets	2.00%		2.00%

[1] Other investments in 2014 and 2013 consist of cash equivalents.