Financial Instruments Descriptions (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014 MMcf	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Interest Rate Hedges, Senior Notes 2013 Issuance [Member]	Aug. 31, 2011 Interest Rate Hedges, Senior Notes 2013 Issuance [Member]	Sep. 30, 2012 Interest Rate Hedges, Short-term Note 2012 Issuance [Member]	Sep. 30, 2014 Interest Rate Hedges, Senior Notes 2015 Issuance [Member]	Sep. 30, 2014 Interest Rate Hedges, Senior Notes 2017 Issuance [Member]	Sep. 30, 2014 Interest Rate Hedges, Senior Notes 2019 Issuance [Member]
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	32.00%
Hedge Volume Of Actual Heating Season Gas	24,800
Weighted Average Cost Of Actual Heating Season Gas	4.02
Minimum Length Of Time Hedged In Cash Flow Hedge	0 years 1 month 0 days
Maximum Length of Time Hedged in Cash Flow Hedge	0 years 61 months 0 days
Net Open Positions	100
Gain Loss On Hedge Ineffectiveness	$ 1.9	$ 18.2	$ 23.1
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	(5.0)	3.0	(2.5)
Natural Gas Inventory [Abstract]
Inventory Write-down			1.7
Derivative [Line Items]
Derivative, Notional Amount					350	260	500	250	400
Anticipated Debt Issuance, Amount									450
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)				$ (66.6)