Rate and Regulatory Matters (Details) $ in Millions	1 Months Ended
Jan. 31, 2023 USD ($)	Jan. 01, 2023 $ / dekatherm
Regulated Operations [Abstract]
Demand Rate		0.37250
Commodity Rate		0.00935
Amount refunded as a result of approved Settlement \| $	$ 126

Amount of refund to customers as a result of approved Settlement with the FERC.

No definition available.

Name:	nwp_RefundAsResultOfSettlement
Namespace Prefix:	nwp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration