Business Segment Information (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Mar. 31, 2013
Utility [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	$ 49.4
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	20.5
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	153.6
All Other [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	48.0
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	$ 59.5