Fair Value of Financial Instruments Financial Assets and Liabilities Recognized at Fair Value (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Estimate of Fair Value, Fair Value Disclosure [Member]
Nuclear decommissioning trust (1):
Money market funds	$ 15	$ 13
Debt securities:
U.S. treasury securities	6	3
Corporate debt securities	6	6
Mortgage-backed securities	5	7
Municipal securities	3	4
Asset-backed securities	2	1
Equity securities:
Mutual funds	10	17
Common stocks	2	2
Debt securities - mutual funds	2	2
Assets from price risk management activities (1) (3):
Electricity	2	5
Natural gas	7	11
Total	60	71
Liabilities - Liabilities from price risk management activities (1) (3):
Electricity	126	119
Natural gas	217	257
Total	343	376
Fair Value, Inputs, Level 1 [Member]
Nuclear decommissioning trust (1):
Money market funds	0	0
Debt securities:
U.S. treasury securities	6	3
Corporate debt securities	0	0
Mortgage-backed securities	0	0
Municipal securities	0	0
Asset-backed securities	0	0
Equity securities:
Mutual funds	9	16
Common stocks	2	2
Debt securities - mutual funds	2	2
Assets from price risk management activities (1) (3):
Electricity	0	0
Natural gas	0	0
Total	19	23
Liabilities - 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	15	13
Debt securities:
U.S. treasury securities	0	0
Corporate debt securities	6	6
Mortgage-backed securities	5	7
Municipal securities	3	4
Asset-backed securities	2	1
Equity securities:
Mutual funds	1	1
Common stocks	0	0
Debt securities - mutual funds	0	0
Assets from price risk management activities (1) (3):
Electricity	2	4
Natural gas	7	11
Total	41	47
Liabilities - Liabilities from price risk management activities (1) (3):
Electricity	90	102
Natural gas	104	153
Total	194	255
Fair Value, Inputs, Level 3 [Member]
Nuclear decommissioning trust (1):
Money market funds	0	0
Debt securities:
U.S. treasury securities	0	0
Corporate debt securities	0	0
Mortgage-backed securities	0	0
Municipal securities	0	0
Asset-backed securities	0	0
Equity securities:
Mutual funds	0	0
Common stocks	0	0
Debt securities - mutual funds	0	0
Assets from price risk management activities (1) (3):
Electricity	0	1
Natural gas	0	0
Total	0	1
Liabilities - Liabilities from price risk management activities (1) (3):
Electricity	36	17
Natural gas	113	104
Total	$ 149	$ 121

Assets from price risk management activities: [Abstract]

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- Definition

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

+ Details

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- Definition

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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- Definition

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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- Definition

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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- Definition

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

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- Definition

Debt securities: [Abstract]

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- Definition

Liabilities from price risk management activities: [Abstract]

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- Definition

Debt mutual funds assets in the Non-qualified benefit plan trust, which are carried at fair value.

+ Details

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- Definition

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

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- Definition

Nuclear decommissioning trust: [Abstract]

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- Definition

Investments in notes or bonds that are collateralized by a specific group of underlying assets owned by the issuer of the notes or bonds 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 8, 9

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

+ Details

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Chapter 4

-Paragraph 80

-Subparagraph Exhibit 4-3

-IssueDate 2006-05-01

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Chapter 4

-Paragraph 38, 40

-IssueDate 2006-05-01

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 320

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6475986&loc=d3e42546-110969

+ Details

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 320

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6475986&loc=d3e42546-110969

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- Definition

This element represents the aggregate of the liabilities reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ Details

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- Details

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- Definition

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.

+ References

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents securitized, pay-through debt securities collateralized by real estate mortgage loans (mortgages) as of the balance sheet date which have been categorized as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-DEP

-Chapter 7

-Paragraph 15

-IssueDate 2006-05-01

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Mortgage-Backed Securities

-URI http://asc.fasb.org/extlink&oid=6517959

+ Details

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- Definition

Bonds or similar securities issued by state, city, or local governments or the agencies operated by state, city, or local governments 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.

+ References

+ Details

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- Definition

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.

+ References

+ Details

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