Price Risk Management Net realized and unrealized gains and losses on derivative transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Commodity contracts:
Electricity	$ 53	$ 31
Natural Gas	$ 36	$ (6)

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:	na
Period Type:	duration