Business Segment Information (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Mar. 31, 2012
Utility [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	$ 64.2
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	387.3
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	$ 90.6