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Revenue Energy Prepayment Agreement (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2018
Long-term Contract for Purchase of Electric Power [Line Items] |  |  |
Proceeds from Maturities, Prepayments and Calls of Other Investments | $ 1,500 |  |
Other Significant Noncash Transaction, Value of Consideration Given | $ 10 | $ 25 | $ 100
Revenue Recognition, Revenue Reductions [Policy Text Block] | 141 | 137 |
Discount to Revenue [Member] |  |  |
Long-term Contract for Purchase of Electric Power [Line Items] |  |  |
Other Significant Noncash Transaction, Value of Consideration Given | $ 4 | $ 11 |

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- Definition The value of the noncash (or part noncash) consideration given (for example, liability, equity) in a transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of a transaction not resulting in cash receipts or cash payments in the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586 + Details
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- Definition The cash inflow associated with the maturity (principal being due), prepayment and call (request of early payment) of other investments not otherwise defined in the taxonomy. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585 + Details
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- Definition Disclosure of accounting policy of sales arrangements for goods or services that reduce the amount of revenue recognized for example sales returns, allowances, incentives, rebates, discounts and loyalty programs. + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790 + Details
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