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Acquisitions and Dispositions of Businesses - Dispositions (Details) | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 USD ($) disposal | Jun. 30, 2017 USD ($) disposal | Jun. 30, 2018 USD ($) disposal | Jun. 30, 2017 USD ($) disposal
Dispositions |  |  |  |
Loss on disposal of business | $ 0 | $ 0 | $ (1,000,000) | $ (2,000,000)
Disposal Group, Not Discontinued Operations |  |  |  |
Dispositions |  |  |  |
Number of dispositions | disposal | 1 | 1 | 1 | 4
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations |  |  |  |
Dispositions |  |  |  |
Disposal group valuation allowances | $ 176,000,000 |  | $ 176,000,000 |
Disposal group assets | 47,000,000 |  | 47,000,000 |
Disposal group liabilities | 41,000,000 |  | 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 |  | $ 176,000,000 |

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