Commitments and Contingencies - Commitments for Construction (Details) $ in Millions	9 Months Ended
Sep. 30, 2026 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Purchase commitments, expected to be settled through the end of 2028	$ 606.3

The minimum amount the entity agreed to spend under the short-term and long-term purchase commitments.

No definition available.

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