Commitments and Contingencies Undivided Interests (Details) - Bistineau Storage - USD ($) $ in Millions	Apr. 01, 2020	Mar. 31, 2020
Undivided Interest Property [Line Items]
Co-owner's interest in storage facility		8.00%
Purchase price to obtain co-owner's interest in storage facility	$ 18.8
Undivided interests in storage facility	100.00%

Purchase price to obtain the co-owner percentage held in the undivided interest in a storage facility.

No definition available.

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