Cash and Cash Equivalents and Short-Term Investments (Details) £ in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($)	Mar. 31, 2023 GBP (£)	Dec. 31, 2022 USD ($)	Dec. 31, 2022 GBP (£)
Cash, Cash Equivalents, and Short-Term Investments [Abstract]
Cash and cash equivalents and short-term investments	$ 1,291.0		$ 1,142.0
Cash and cash equivalents and short term investments, period increase (decrease)	149.0
Restricted cash and investments	117.0		115.0
Operating funds required to be held in U.K.	$ 76.8	£ 62.8	$ 72.5	£ 60.1