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Impairments (Details) - USD ($) |  | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | ---
Jun. 29, 2018 | Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017
Impaired Long-Lived Assets Held and Used [Line Items] |  |  |  |  |  |
Ownership interest | 3.70% |  |  |  |  |
Carrying amount of related assets |  | $ 1,055,000,000 |  | $ 1,055,000,000 |  | $ 1,038,000,000
Impairment losses |  | 74,000,000 | $ 63,000,000 | 74,000,000 | $ 63,000,000 |
Construction in progress |  |  | 0 |  | $ 0 |
Renewables |  |  |  |  |  |
Impaired Long-Lived Assets Held and Used [Line Items] |  |  |  |  |  |
Impairment losses |  |  | 22,000,000 |  |  |
Construction in Progress |  |  |  |  |  |
Impaired Long-Lived Assets Held and Used [Line Items] |  |  |  |  |  |
Impairment losses |  |  | $ 41,000,000 |  |  |
Keystone |  |  |  |  |  |
Impaired Long-Lived Assets Held and Used [Line Items] |  |  |  |  |  |
Impairment losses to reduce carrying amounts | $ 14,000,000 |  |  |  |  |
Conemaugh |  |  |  |  |  |
Impaired Long-Lived Assets Held and Used [Line Items] |  |  |  |  |  |
Impairment losses to reduce carrying amounts | $ 14,000,000 |  |  |  |  |
Dunkirk |  |  |  |  |  |
Impaired Long-Lived Assets Held and Used [Line Items] |  |  |  |  |  |
Impairment losses to reduce carrying amounts |  | 46,000,000 |  |  |  |
Carrying amount of related assets |  | $ 0 |  | $ 0 |  |

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- Definition Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
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- Definition Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
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- Definition This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 35 -Paragraph 32 -URI http://asc.fasb.org/extlink&oid=99375318&loc=d3e32787-111569 + Details
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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571 + Details
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- Definition This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=66022249&loc=d3e33749-111570 Reference 2: 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 + Details
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