Commitments and Contingencies Environmental Liabilities (Details) $ in Millions	Dec. 31, 2019 USD ($)
Environmental remediation obligations [Member]
Environmental remediation obligation, minimum	$ 29.2
Environmental remediation obligation, maximum	31.9
Accrual for environmental loss contingencies	30.3
Combined Manufacturing Sites [Member] \| Manufactured Gas Plants [Member]
Accrual for environmental loss contingencies	24.5
Aberdeen South Dakota Site [Member] \| Manufactured Gas Plants [Member]
Accrual for environmental loss contingencies	8.2
Environmental remediation obligation, to be incurred during next 5 years	$ 2.9

Total costs accrued as of the balance sheet date for environmental loss contingencies.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14326-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 25
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346

Reference 3: 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

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