Fair Value Measurements - Assets and Liabilities Measured on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 250.5	$ 902.1
Restricted cash	396.1	168.4
Short-term investment securities	0.0	118.3
Assets held for sale	3.1	463.0
Total assets	649.7	1,651.8
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	250.5	902.1
Restricted cash	396.1	168.4
Short-term investment securities	0.0	118.3
Assets held for sale	0.0	0.0
Total assets	646.6	1,188.8
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	3.1	463.0
Total assets	3.1	463.0
Total liabilities	$ 0.0	$ 0.0