Fair Value of Financial Instruments Financial Assets and Liabilities Recognized at Fair Value (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Nuclear decommissioning trust: (1)
Money market funds	$ 65us-gaap_MoneyMarketFundsAtCarryingValue	$ 65us-gaap_MoneyMarketFundsAtCarryingValue
Debt securities:
Domestic government	14	14
Corporate credit	11	11
Equity securities:
Domestic	6por_MutualFundsEquity	5por_MutualFundsEquity
International	1	1
Assets from price risk management activities: (1) (3)
Electricity	7por_CommodityContractAssetElectricity	5por_CommodityContractAssetElectricity
Natural gas	2por_CommodityContractAssetNaturalGas	2por_CommodityContractAssetNaturalGas
Total	106	103
Liabilities from price risk management activities: (1) (3)
Electricity	138	112
Natural gas	145	116
Total	283us-gaap_LiabilitiesFairValueDisclosure	228us-gaap_LiabilitiesFairValueDisclosure
Fair Value, Inputs, Level 1 [Member]
Nuclear decommissioning trust: (1)
Money market funds	0	0
Debt securities:
Domestic government	4	7
Corporate credit	0	0
Equity securities:
Domestic	5	4
International	1	1
Assets from price risk management activities: (1) (3)
Electricity	0	0
Natural gas	0	0
Total	10	12
Liabilities from price risk management activities: (1) (3)
Electricity	0	0
Natural gas	0	0
Total	0	0
Fair Value, Inputs, Level 2 [Member]
Nuclear decommissioning trust: (1)
Money market funds	65	65
Debt securities:
Domestic government	10	7
Corporate credit	11	11
Equity securities:
Domestic	1	1
International	0	0
Assets from price risk management activities: (1) (3)
Electricity	5	4
Natural gas	2	2
Total	94	90
Liabilities from price risk management activities: (1) (3)
Electricity	24	32
Natural gas	109	95
Total	133	127
Fair Value, Inputs, Level 3 [Member]
Nuclear decommissioning trust: (1)
Money market funds	0	0
Debt securities:
Domestic government	0	0
Corporate credit	0	0
Equity securities:
Domestic	0	0
International	0	0
Assets from price risk management activities: (1) (3)
Electricity	2	1
Natural gas	0	0
Total	2	1
Liabilities from price risk management activities: (1) (3)
Electricity	114	80
Natural gas	36	21
Total	$ 150	$ 101

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Carrying amount as of the balance sheet date of the asset arising from commodity contracts related to purchases or sales of electricity.

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Carrying amount as of the balance sheet date of the asset arising from commodity contracts related to purchases or sales of natural gas.

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Carrying amount as of the balance sheet date of the liabilities arising from commodity contracts related to purchases or sales of electricity.

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Carrying amount as of the balance sheet date of the liabilities arising from commodity contracts related to purchases or sales of natural gas.

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Common stock asset securities held in Non-qualified benefit plan trust, which are carried at fair value

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Equity mutual fund assets held in the Non-qualified benefit plan trust, which are carried at fair value.

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The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings.

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-Name Accounting Standards Codification

-Topic 940

-SubTopic 320

-Section 45

-Paragraph 2

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The fair value as of the balance sheet date of firm holdings in fixed income or other debt securities issued by a corporation or other issuer not elsewhere specified in the taxonomy. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

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Fair value of financial and nonfinancial obligations.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

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Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

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Debt (bills, notes or bonds) that are issued by the government of the United States which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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