Cash and Cash Equivalents and Short-Term Investments (Details) £ in Millions, $ in Millions	6 Months Ended
	Jun. 30, 2022 USD ($)	Jun. 30, 2022 GBP (£)	Dec. 31, 2021 USD ($)	Dec. 31, 2021 GBP (£)
Cash, Cash Equivalents, and Short-Term Investments [Abstract]
Cash and cash equivalents and short-term investments	$ 983.0		$ 836.0
Cash and cash equivalents and short term investments, period increase (decrease)	147.0
Restricted cash and investments	153.0		160.0
Operating funds required to be held in U.K.	$ 103.4	£ 84.3	$ 112.8	£ 84.3