Commitments and Contingencies Letter of Credit Proceeds (Details) $ in Millions	9 Months Ended
Sep. 30, 2019 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Letter of Credit Proceeds	$ 27.7
Letter of Credit Proceeds Recognized into Transportation Revenue	$ 26.2

Amount of Letter of Credit proceeds recognized into transportation revenue.

No definition available.

Name:	bwp_LetterofCreditProceedsRecognizedintoTransportationRevenue
Namespace Prefix:	bwp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration