XML 103 R135.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2

FERC (Details 6) $ in Millions	Jan. 01, 2020 USD ($)
Montana-Dakota Utilities Co. [Member] | Electricity [Member] | Subsequent Event [Member] | MISO [Member]
Public Utilities, General Disclosures [Line Items]
Transmission Formula Revenue Requirement	$ 13.1

X

- Definition

Transmission Formula Revenue Requirement

+ References

No definition available.

+ Details

Name:	mdu_TransmissionFormulaRevenueRequirement
Namespace Prefix:	mdu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

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.

+ References

No definition available.

+ Details

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

X

- Details

Name:	dei_LegalEntityAxis=mdu_MontanaDakotaUtilitiesCo.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_PublicUtilityAxis=us-gaap_ElectricityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RegulatoryAgencyAxis=mdu_MISOMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: