Regulatory Matters (Narrative) (Details) $ in Millions	12 Months Ended
Sep. 30, 2018 USD ($)
Regulatory Matters [Line Items]
Required Temporary Refund on Customer Rates	2.20%
Approved Return on Equity	8.70%
Empire [Member]
Regulatory Matters [Line Items]
Proposed Annual Cost of Service	$ 71.5
Proposed Rate Base	$ 246.8
Proposed Return on Equity	14.00%
2017 Tax Reform Act Regulatory Refund [Member] \| New York [Member]
Regulatory Matters [Line Items]
Refund Provision Associated with Impact of 2017 Tax Reform	$ 9.1
2017 Tax Reform Act Regulatory Refund [Member] \| Pennsylvania [Member]
Regulatory Matters [Line Items]
Refund Provision Associated with Impact of 2017 Tax Reform	$ 3.4

Amount of expenses incurred but not yet paid classified as other, due within one year or the normal operating cycle, if longer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6911-107765

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e7018-107765

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6935-107765

Name:	us-gaap_OtherAccruedLiabilitiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant