Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

FERC (Details 7) - USD ($) $ in Millions	Jan. 01, 2020	May 01, 2019
FERC [Member] \| Gas Distribution [Member] \| WBI Energy Transmission, Inc. [Member] \| Tax Cuts and Jobs Act [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 4.5
MISO [Member] \| Electricity [Member] \| Montana-Dakota Utilities Co. [Member] \| Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Transmission Formula Revenue Requirement	$ 13.4