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Regulatory Matters (Schedule of COVID-19 Regulatory Impact) (Details) $ in Millions	Mar. 31, 2021 USD ($)
Incremental O&M - COVID | Columbia Of Ohio
Regulated Operations
Regulatory Assets	$ 2.0
Incremental O&M - COVID | Columbia Of Virginia
Regulated Operations
Regulatory Assets	0.1
Incremental O&M and Bad Debt - COVID | NIPSCO
Regulated Operations
Regulatory Assets	12.0
Incremental O&M and Bad Debt - COVID | Columbia Of Maryland
Regulated Operations
Regulatory Assets	1.1
Incremental Bad Debt - COVID | Columbia Of Pennsylvania
Regulated Operations
Regulatory Assets	$ 7.1

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- Definition

Regulated Operations

+ References

No definition available.

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- Definition

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

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