Balance Sheet Accounts - Schedule of Other Current Assets (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred costs recoverable from the U.S. government	$ 40.2	$ 41.0
Income tax receivable	30.1	46.9
Inventories	11.5	10.0
Prepaid expenses	17.5	18.0
Other	22.0	20.6
Other current assets	$ 121.3	$ 136.5

Amount of asset related to consideration paid in advance for costs that provide economic benefits within a future period of one year or the normal operating cycle, if longer.

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