Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Goodwill (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Mar. 16, 2020
Goodwill [Line Items]
Goodwill	$ 2,340,836		$ 2,324,547
Peoples Gas Acquisition [Member]
Goodwill [Line Items]
Goodwill		$ 16,400		$ 2,277,447
Natural Gas Utility [Member] \| Peoples Gas Acquisition [Member]
Goodwill [Line Items]
Goodwill				$ 2,277,447