Summary of Significant Accounting Policies - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	$ (216.8)	$ (181.4)
Unrealized losses on defined benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	(23.4)	(27.3)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	$ (240.2)	$ (208.7)

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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+ Details