Price Risk Management Net realized and unrealized gains and losses on derivative transactions (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivative [Line Items]
Net gain or loss recognized in the statement of income offset by regulatory accounting	$ 192	$ 258	$ 98
Commodity contracts: [Abstract]
Commodity Contracts, Electricity	117	127	79
Contracts, Natural Gas	$ 98	$ 192	$ 101

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