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Fair Value of Assets and Liabilities - Narrative (Details) - Corporate - USD ($) | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Segment Reporting Information [Line Items] |  |  |  |
Fixed asset impairments | $ 1,000,000 | $ 0 | $ 33,000,000 | $ 1,000,000
Asset impairment charges |  |  | 33,000,000 |
Disposition of Acquired Properties | 2019 Business Optimization |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Asset impairment charges | $ 0 | $ 0 | $ 3,000,000 | $ 0

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