Basis of Presentation (Details)	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Percent of General Partner Interest Owned by Holding Company (in hundredths)	100.00%

The percent of the general partner interest owned by the holding company.

No definition available.

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