Regulatory Matters: TCJA (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2020
Regulated Operations [Abstract]
Income Tax Benefit from Relieved TCJA Related Liabilities	$ 3,500	$ 4,000

Income Tax Benefit from Relieved TCJA Related Liabilities

No definition available.

Name:	bhp_IncomeTaxBenefitFromRelievedTCJARelatedLiabilities
Namespace Prefix:	bhp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration