Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Name:	us-gaap_GoodwillImpairmentLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Goodwill (Narrative) (Details) - USD ($)	9 Months Ended
Goodwill (Narrative) (Details) - USD ($)	Sep. 30, 2020	Mar. 16, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill impairment	$ 0
Goodwill	$ 2,333,627,000		$ 63,822,000
Peoples Gas Acquisition [Member]
Goodwill [Line Items]
Goodwill		$ 2,267,310,000
Natural Gas Utility [Member] \| Peoples Gas Acquisition [Member]
Goodwill [Line Items]
Goodwill		$ 2,267,310,000