Utility Regulatory Assets and Liabilities and Regulatory Matters - Regulatory Assets and Liabilities Associated with Utilities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Regulatory Assets and Liabilities
Regulatory assets	$ 268.2	$ 244.9
Regulatory liabilities	32.5	37.3
Postretirement Benefits
Regulatory Assets and Liabilities
Regulatory liabilities	18.6	16.5
Environmental Overcollections
Regulatory Assets and Liabilities
Regulatory liabilities	0.3	2.6
Deferred Fuel and Power Refunds
Regulatory Assets and Liabilities
Regulatory liabilities	0.3	8.3
State Tax Benefits - Distribution System Repairs
Regulatory Assets and Liabilities
Regulatory liabilities	10.1	8.4
Other Regulatory Liabilities
Regulatory Assets and Liabilities
Regulatory liabilities	3.2	1.5
Income Taxes Recoverable
Regulatory Assets and Liabilities
Regulatory assets	110.7	106.1
Underfunded Pension and Postretirement Plans
Regulatory Assets and Liabilities
Regulatory assets	110.1	94.5
Environmental Costs
Regulatory Assets and Liabilities
Regulatory assets	14.6	17.1
Deferred Fuel and Power Costs
Regulatory Assets and Liabilities
Regulatory assets	11.8	8.3
Removal Costs, Net
Regulatory Assets and Liabilities
Regulatory assets	16.8	13.3
Other Regulatory Assets
Regulatory Assets and Liabilities
Regulatory assets	$ 4.2	$ 5.6