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Income Taxes - The Tax Cuts and Jobs Act (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Mar. 31, 2017 | Sep. 30, 2018 | Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2016 | Jun. 30, 2017
Income taxes |  |  |  |  |  |  |  |  |
Federal corporate tax rate (as a percent) |  |  | 35.00% |  | 21.00% | 24.50% | 35.00% | 35.00% |
Provisional income tax benefit related to deferred tax assets and liabilities |  |  |  |  |  | $ 32.0 |  |  |
Undistributed earnings from foreign subsidiaries | $ 79.8 |  |  |  | $ 79.8 | 79.8 |  |  |
One-time transition tax on accumulated foreign earnings |  |  |  |  |  | 64.0 |  |  |
Valuation allowance | 197.1 |  |  |  | 197.1 | 197.1 | $ 138.4 |  |
Change in valuation allowance |  |  |  |  |  | 58.7 |  |  |
Amount of uncertain tax positions for future years | 27.7 | $ 26.2 |  |  |  |  |  |  |
Benefits related to excess foreign tax credits expected to be realized |  |  |  |  |  |  | $ 25.2 |  |
United States |  |  |  |  |  |  |  |  |
Income taxes |  |  |  |  |  |  |  |  |
Valuation allowance | 38.1 |  |  |  | 38.1 | 38.1 |  |  |
Canada |  |  |  |  |  |  |  |  |
Income taxes |  |  |  |  |  |  |  |  |
Valuation allowance | 13.1 |  |  |  | $ 13.1 | $ 13.1 |  |  |
Change in valuation allowance | $ 13.1 |  |  |  |  |  |  |  |
United Kingdom |  |  |  |  |  |  |  |  |
Income taxes |  |  |  |  |  |  |  |  |
Change in valuation allowance |  |  |  | $ (59.9) |  |  |  |  |
Europe |  |  |  |  |  |  |  |  |
Income taxes |  |  |  |  |  |  |  |  |
Benefit due to reinvesting portion of undistributed earnings |  |  |  |  |  |  |  |  | $ 21.2

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