Financial Instruments Descriptions (Details) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) MMcf	Jun. 30, 2014 USD ($)
General Discussion Of Derivative Instruments And Hedging Activities [Abstract]
Minimum Hedge Percentage Of Anticipated Heating Season Gas			25.00%
Maximum Hedge Percentage Of Anticipated Heating Season Gas			50.00%
Hedge Percentage Of Actual Heating Season Gas			37.00%
Hedge Volume Of Actual Heating Season Gas | MMcf			28,200
Minimum Length Of Time Hedged In Cash Flow Hedge	1 month
Maximum Length Of Time Hedged In Cash Flow Hedge	52 months
Accumulated Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Interest Rate Agreements, Realized Gain (Loss), Net of Tax	$ (18.7)		$ (18.7)
Gain (Loss) On Hedge Ineffectiveness	3.6	$ (0.1)	$ (0.9)	$ 1.3
Regulated Segments Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate			37.00%
Nonregulated Segment Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate			39.00%
Gain (Loss) On Derivative Instruments Not Designated Hedges Net Pretax	3.7	$ (0.6)	$ 13.2	$ (10.7)
Interest Rate Hedges, Senior Notes 2017 Issuance [Member]
Derivative [Line Items]
Notional Amount of Interest Rate Cash Flow Hedge Derivatives	250.0		250.0
Anticipated Debt Issuance, Amount	$ 250.0		$ 250.0
Derivative, Average Forward Interest Rate	3.37%		3.37%
Interest Rate Hedges, Senior Notes 2019 Issuance [Member]
Derivative [Line Items]
Notional Amount of Interest Rate Cash Flow Hedge Derivatives	$ 450.0		$ 450.0
Anticipated Debt Issuance, Amount	$ 450.0		$ 450.0
Derivative, Average Forward Interest Rate	3.78%		3.78%