Business Segment Information (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Jun. 30, 2012
Utility [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	$ 28.9
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	23.1
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	474.4
All Other [Member]
Segment Reporting Information [Line Items]
Increase in segment assets	$ 35.9