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Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities, Cost and Fair Value of Rabbi Trusts (Details) - Fair Value Measured on a Recurring Basis - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Cost |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt Securities, Trading, and Equity Securities, FV-NI | [1] | $ 68 | $ 59
Cost | Rabbi Trust [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and Cash Equivalents, Fair Value Disclosure | [1] | 16 | 12
Cost | Mutual Funds [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt Securities, Trading, and Equity Securities, FV-NI | [1] | 52 | 47
Fair Value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt Securities, Trading, and Equity Securities, FV-NI | [1] | 67 | 62
Fair Value | Level 1 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt Securities, Trading, and Equity Securities, FV-NI | [1] | 67 | 62
Fair Value | Level 2 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt Securities, Trading, and Equity Securities, FV-NI |  | 0 | 0
Fair Value | Level 3 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt Securities, Trading, and Equity Securities, FV-NI | [1] | 0 | 0
Fair Value | Rabbi Trust [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and Cash Equivalents, Fair Value Disclosure | [1] | 16 | 12
Fair Value | Rabbi Trust [Member] | Level 1 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and Cash Equivalents, Fair Value Disclosure | [1] | 16 | 12
Fair Value | Rabbi Trust [Member] | Level 2 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and Cash Equivalents, Fair Value Disclosure | [1] | 0 | 0
Fair Value | Rabbi Trust [Member] | Level 3 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and Cash Equivalents, Fair Value Disclosure | [1] | 0 | 0
Fair Value | Mutual Funds [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt Securities, Trading, and Equity Securities, FV-NI | [1] | 51 | 50
Fair Value | Mutual Funds [Member] | Level 1 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt Securities, Trading, and Equity Securities, FV-NI | [1] | 51 | 50
Fair Value | Mutual Funds [Member] | Level 2 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt Securities, Trading, and Equity Securities, FV-NI | [1] | 0 | 0
Fair Value | Mutual Funds [Member] | Level 3 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt Securities, Trading, and Equity Securities, FV-NI | [1] | $ 0 | $ 0
[1] | d in nuclear decommissioning fund and other investments on the consolidated balance sheet.

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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes 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. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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