Commitments And Contingencies (Narrative) (Details) $ in Millions	12 Months Ended
	Sep. 30, 2016 USD ($)
Site Contingency [Line Items]
Estimate minimum liability for environmental remediation	$ 4.5
Future purchase obligation first year	241.2
Future purchase obligation second year	96.5
Future purchase obligation third year	94.7
Future purchase obligation fourth year	95.3
Future purchase obligation fifth year	83.8
Future purchase obligation thereafter	794.4
Operating lease commitment first year	13.7
Operating lease commitment second year	5.8
Operating lease commitment third year	4.2
Operating lease commitment fourth year	3.0
Operating lease commitment fifth year	1.5
Operating lease commitment thereafter	0.4
Former Manufactured Gas Plant Site [Member]
Site Contingency [Line Items]
Estimate minimum liability for environmental remediation	$ 2.8
Environmental Site Remediation Costs [Member]
Site Contingency [Line Items]
Rate recovery period	12 years
Exploration And Production [Member]
Site Contingency [Line Items]
Contract commitments first year	$ 25.2
Pipeline And Storage And Gathering Segments [Member]
Site Contingency [Line Items]
Contract commitments first year	52.5
Contract commitments second year	7.2
Contract commitments third year	0.1
Contractual commitments fourth year	0.1
Contractual commitments fifth year	0.1
Contractual commitments thereafter	$ 0.5