Basis of Presentation (Details)	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Percentage of Company's Interest Directly and Indirectly Owned by Holding Company	100.00%

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

No definition available.

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