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Acquisitions and Dispositions of Businesses - Dispositions (Details) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 USD ($) disposal | Jun. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) disposal | Sep. 30, 2018 USD ($) disposal | Sep. 30, 2017 USD ($) disposal
Dispositions |  |  |  |  |
Gain (loss) on disposal of business | $ (3,000,000) |  | $ 0 | $ (4,000,000) | $ (2,000,000)
Disposal Group, Not Discontinued Operations |  |  |  |  |
Dispositions |  |  |  |  |
Number of dispositions | disposal | 2 |  | 0 | 3 | 4
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations |  |  |  |  |
Dispositions |  |  |  |  |
Disposal group assets |  | $ 47,000,000 |  |  |
Disposal group liabilities |  | 41,000,000 |  |  |
Amortization And Impairment Of Intangible Assets | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations |  |  |  |  |
Dispositions |  |  |  |  |
Impairment loss |  | $ 176,000,000 |  | $ 175,000,000 |

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