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Fair Value of FInancial Instruments Schedule of Fair Value (Details) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Money market funds | $ 21 | $ 18
Domestic government, Debt securities | 12 | 14
Corporate debt securities held in decommissioning trust assets | 8 | 8
Fair Value - Money market funds | 1 | 0
Domestic Equity Securities | 4 | 3
Debt securities - domestic government | 1 | 1
Alternative Investments, Fair Value Disclosure |  | 1
Investments, Fair Value Disclosure | 2 | 2
Electricity | 7 | 7
Natural gas | 16 | 3
Liabilities from price risk management activities: [Abstract] |  |
Electricity | 118 | 133
Natural gas | 51 | 158
Liabilities, Fair Value Disclosure | 169 | 291
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] |  |
Assets, Fair Value Disclosure | 72 | 57
Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Domestic government, Debt securities | 2 | 6
Corporate debt securities held in decommissioning trust assets | 0 | 0
Fair Value - Money market funds | 1 | 0
Domestic Equity Securities | 4 | 3
Debt securities - domestic government | 1 | 1
Electricity | 0 | 0
Natural gas | 0 | 0
Liabilities from price risk management activities: [Abstract] |  |
Electricity | 0 | 0
Natural gas | 0 | 0
Liabilities, Fair Value Disclosure | 0 | 0
Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Domestic government, Debt securities | 10 | 8
Corporate debt securities held in decommissioning trust assets | 8 | 8
Fair Value - Money market funds | 0 | 0
Domestic Equity Securities | 0 | 0
Debt securities - domestic government | 0 | 0
Electricity | 6 | 7
Natural gas | 15 | 3
Liabilities from price risk management activities: [Abstract] |  |
Electricity | 6 | 28
Natural gas | 42 | 144
Liabilities, Fair Value Disclosure | 48 | 172
Fair Value, Inputs, Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Money market funds | 0 |
Domestic government, Debt securities | 0 | 0
Corporate debt securities held in decommissioning trust assets | 0 | 0
Fair Value - Money market funds |  | 0
Domestic Equity Securities | 0 | 0
Debt securities - domestic government | 0 | 0
Electricity | 1 | 0
Natural gas | 1 | 0
Liabilities from price risk management activities: [Abstract] |  |
Electricity | 112 | 105
Natural gas | 9 | 14
Liabilities, Fair Value Disclosure | 121 | 119
Non Qualified Benefit Plans [Member] |  |
Liabilities from price risk management activities: [Abstract] |  |
Insurance contracts, at cash surrender value | $ 26 | $ 26

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- Definition Fair value of investments in certain entities that calculate net asset value per share, including, but not limited to, by unit, membership interest, or other ownership interest. Investments include, but are not limited to, investments in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258 + Details
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- Definition Fair value portion of the amount that could be realized under a life insurance contract or contracts owned by the entity, commonly known as corporate-owned life insurance (COLI) or bank-owned life insurance (BOLI). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Surrender Value -URI http://asc.fasb.org/extlink&oid=6507153 + Details
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- Definition Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(12)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(5)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(2)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(1)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 9: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594 + 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 Reference 1: 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 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 Reference 1: 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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