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Income Taxes - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Tax Credit Carryforward [Line Items] |  |  |  |
GILTI | $ (1,143.7) | $ (1,381.6) |  |
Income taxes paid | 62.0 |  |  |
Deferred tax liabilities, temporary differences, purchase accounting, foreign subsidiaries | 1,500.0 |  |  |
Total deferred charges and prepaid taxes | 142.2 | 243.8 |  |
Valuation allowance | 1,753.9 | 1.1 |  |
Other | 103.1 | 103.7 |  |
Unrecognized tax benefit | 68.8 | 122.7 | $ 109.1 |
Net interest expense | 1.0 | 4.7 | 2.2 |
Unrecognized tax benefits, interest on income taxes accrued | 21.2 | 20.0 |  |
Decrease in unrecognized tax benefits is reasonably possible | 25.0 |  |  |
2017 Tax Act |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |
Reduction in deferred tax liability, undistributed foreign earnings |  |  | 34.6 |
Income tax expense (benefit) |  |  | 12.7 |
GILTI |  |  | 135.8 |
Other tax expense (benefit) |  |  | $ 11.0 |
Transition toll tax liabilities | 697.0 | 697.0 |  |
General Business | Domestic Country |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |
Operating loss carryforwards | 0.6 |  |  |
Tax credit carryforward, amount | 1.3 |  |  |
Operating loss carryforward, subject to expiration | 18,000.0 |  |  |
General Business | Foreign Tax Authority |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |
Operating loss carryforward, subject to expiration | 16,800.0 |  |  |
Research | State and Local Jurisdiction |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |
Tax credit carryforward, amount | 142.4 |  |  |
Earnings in the form of cash and cash equivalents | 2017 Tax Act |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |
Transition toll tax repatriation tax rate |  |  |  | 15.50%
Other Foreign Earnings | 2017 Tax Act |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |
Transition toll tax repatriation tax rate |  |  |  | 8.00%
Minimum |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |
Residual U.S. tax liability on reversal of deferred tax liabilities on foreign subsidiaries purchase accounting | 300.0 |  |  |
Maximum |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |
Residual U.S. tax liability on reversal of deferred tax liabilities on foreign subsidiaries purchase accounting | 400.0 |  |  |
Denmark Manufacturing Operations |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |
Tax expense on disposal group |  | 68.9 |  |
TECFIDERA |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |
Deferred tax assets, value, reduction in value | 1,700.0 |  |  |
Deferred tax liabilities, value, reduction in value | 1,600.0 |  |  |
Income tax expense, reduction in deferred tax assets and liabilities, net | $ 90.3 |  |  |
Intellectual Property |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |
Other |  | 754.1 |  |
Deferred tax liabilities, other |  | $ 603.3 |  |

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