Utility Regulatory Assets and Liabilities and Regulatory Matters (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Minimum
Regulatory Assets and Liabilities
Average remaining depreciable lives of the associated property	1 year
Maximum
Regulatory Assets and Liabilities
Average remaining depreciable lives of the associated property	65 years
Environmental Costs
Regulatory Assets and Liabilities
Regulatory asset, amortization period	5 years
Gas Utility
Regulatory Assets and Liabilities
Fair value of unrealized gains (losses)	$ 3.3	$ 1.4
Electric Utility Electric Supply Contracts
Regulatory Assets and Liabilities
Fair value of unrealized gains (losses)	$ (0.5)	$ 0.3
Removal Costs, Net | Maximum
Regulatory Assets and Liabilities
Regulatory asset, amortization period	5 years
Other Regulatory Assets | Minimum
Regulatory Assets and Liabilities
Regulatory asset, amortization period	1 year
Other Regulatory Assets | Maximum
Regulatory Assets and Liabilities
Regulatory asset, amortization period	20 years