Risk Management Net volumes related to price risk management activities (Details) MWh in Millions, MMBTU in Millions, $ in Millions	Sep. 30, 2018 CAD ($) MMBTU MWh	Dec. 31, 2017 CAD ($) MMBTU MWh
Commodity contracts:
Electricity \| MWh	6	7
Natural gas \| MMBTU	115	114
Foreign currency \| $	$ 20	$ 21

Net amount associated with the reporting entity's derivative instruments recorded as of the balance sheet date having arisen from price risk management activities related to foreign currency.

No definition available.

Name:	por_VolumeRelatedtoDerivativeInstrumentsHeldatBalanceSheetDateForeignCurrency
Namespace Prefix:	por_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant