Commitments And Contingencies (Narrative) (Details) $ in Millions	12 Months Ended
	Sep. 30, 2018 USD ($)
Site Contingency [Line Items]
Estimate minimum liability for environmental remediation	$ 7.6
Project Costs	76.2
Future purchase obligation first year	297.9
Future purchase obligation second year	102.9
Future purchase obligation third year	86.6
Future purchase obligation fourth year	152.5
Future purchase obligation fifth year	162.8
Future purchase obligation thereafter	1,606.0
Operating lease commitment first year	18.6
Operating lease commitment second year	4.6
Operating lease commitment third year	4.0
Operating lease commitment fourth year	3.2
Operating lease commitment fifth year	2.7
Operating lease commitment thereafter	12.4
Former Manufactured Gas Plant Site New York [Member]
Site Contingency [Line Items]
Estimate minimum liability for environmental remediation	$ 4.1
Environmental Site Remediation Costs [Member]
Site Contingency [Line Items]
Rate recovery period	4 years
Pipeline And Storage, Gathering And Utility Segments [Member]
Site Contingency [Line Items]
Contract commitments first year	$ 105.1
Contract commitments second year	6.8
Contract commitments third year	6.1
Contractual commitments fourth year	5.1
Contractual commitments fifth year	3.4
Contractual commitments thereafter	13.3
Exploration And Production [Member]
Site Contingency [Line Items]
Contract commitments first year	86.2
Contract commitments second year	$ 24.8