Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Comprehensive income:
Net income	$ 306.6	$ 240.9
Other comprehensive (loss) income:
Foreign currency translation loss included in net income	2.4	0.0
Defined benefit pension plan:
Actuarial loss arising during period, net of tax	(0.5)	(0.9)
Actuarial gain and prior service cost included in net periodic pension cost, net of tax	(1.2)	(2.3)
Total defined benefit pension plan, net of tax	(1.7)	(3.2)
Available-for-sale debt securities:
Unrealized (loss) gain arising during period, net of tax	(4.6)	19.9
Realized loss included in net income, net of tax	1.1	0.0
Total (loss) gain on available-for-sale debt securities, net of tax	(3.5)	19.9
Other comprehensive (loss) income, net of tax	(2.8)	16.7
Comprehensive income	$ 303.8	$ 257.6