CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Comprehensive income:
Net (loss) income	$ (494.6)	$ 244.5
Defined benefit pension plan:
Amortization of actuarial gain and prior service cost included in net periodic pension cost, net of tax	0.1	0.3
Total defined benefit pension plan, net of tax	0.1	0.3
Unrealized gain (loss) on available-for-sale securities, net of tax	2.6	(2.4)
Other comprehensive income (loss), net of tax	2.7	(2.1)
Comprehensive (loss) income	$ (491.9)	$ 242.4