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.

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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.

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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.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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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.

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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.

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Impairments (Details) - USD ($)		3 Months Ended		6 Months Ended
Impairments (Details) - USD ($)	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