MGP, Landfill and Disposal Sites (Details) $ in Millions	9 Months Ended
Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Ashland MGP Site
Ashland Manufactured Gas Plant (MGP) Site [Abstract]
Current Cost Estimate for Site Remediation	$ 199.1
Accrual for Environmental Loss Contingencies, Gross	$ 20.2	$ 23.2
Carrying cost percentage to be applied to unamortized regulatory asset	3.00%
Other MGP, Landfill, or Disposal Sites [Domain]
Ashland Manufactured Gas Plant (MGP) Site [Abstract]
Number of identified MGP sites under current investigation and/or remediation	2

Undiscounted amount of the accrual for environmental loss contingencies.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 5.Y.Q1)
-URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

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