Net realized and unrealized gains and losses on derivative transactions (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commodity contracts: [Abstract]
Electricity	$ 41	$ 34	$ 72
Natural Gas	85	(56)	103
Realized And Unrealized Losses Net Commodity Contracts, Foreign Currency	$ (1)	$ 0	$ 1

Realized and unrealized gains and losses, net on commodity contracts related to electricity not designated as hedging instruments included in purchased power and fuel expense in the statement of income.

No definition available.

Name:	por_RealizedAndUnrealizedGainsAndLossesNetCommodityContractsElectricity
Namespace Prefix:	por_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration