Basis of Presentation (Details)	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Percentage of Company's Capital Directly and Indirectly Owned by Holding Company	100.00%

The percentage of the Company's capital directly and indirectly owned by BPHC.

No definition available.

Name:	bwp_PercentageofCompanysCapitalDirectlyandIndirectlyOwnedbyHoldingCompany
Namespace Prefix:	bwp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant