Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring basis - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 1,333.5	$ 1,789.7
Restricted cash	95.4	71.4
Short-term investment securities	106.3	106.3
Assets held for sale	2.5	2.3
Total assets	1,537.7	1,969.7
Total liabilities	0.0	0.0
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	1,333.5	1,789.7
Restricted cash	95.4	71.4
Short-term investment securities	106.3	106.3
Assets held for sale	0.0	0.0
Total assets	1,535.2	1,967.4
Total liabilities	0.0	0.0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0.0	0.0
Restricted cash	0.0	0.0
Short-term investment securities	0.0	0.0
Assets held for sale	0.0	0.0
Total assets	0.0	0.0
Total liabilities	0.0	0.0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0.0	0.0
Restricted cash	0.0	0.0
Short-term investment securities	0.0	0.0
Assets held for sale	2.5	2.3
Total assets	2.5	2.3
Total liabilities	$ 0.0	$ 0.0