Consolidated Statement of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	Common stock	Retained earnings	Accumulated other comprehensive income (loss)
Equity, beginning balance at Dec. 31, 2020	$ 1,959.8	$ 941.1	$ 962.1	$ 56.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	51.4	0.0	51.4	0.0
Other comprehensive income (loss), net of tax expense	(49.9)	0.0	0.0	(49.9)
Common stock transactions:
Common shares purchased and retired	$ (5.4)	(5.4)	0.0	0.0
Common shares issued (in shares)	604
Common shares issued	$ 0.0	0.0	0.0	0.0
Non-vested common shares issued	0.0	0.0	0.0	0.0
Non-vested common shares forfeited or canceled	0.4	(0.4)	0.0	0.0
Stock options exercised, net of share tendered in payment of option price and income tax withholding amounts	2.4	2.4	0.0	0.0
Stock-based compensation expense	(25.3)	0.0	(25.3)	0.0
Equity, ending balance at Mar. 31, 2021	1,933.4	938.5	988.2	6.7
Equity, beginning balance at Dec. 31, 2021	1,986.6	945.0	1,052.6	(11.0)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(33.4)	0.0	(33.4)	0.0
Other comprehensive income (loss), net of tax expense	(191.0)	0.0	0.0	(191.0)
Common stock transactions:
Common shares purchased and retired	$ (1.4)	(1.4)	0.0	0.0
Common shares issued (in shares)	46,887,104
Common shares issued	$ 1,722.5	1,722.5	0.0	0.0
Non-vested common shares issued	0.0	0.0	0.0	0.0
Non-vested common shares forfeited or canceled	0.0	0.0	0.0	0.0
Stock options exercised, net of share tendered in payment of option price and income tax withholding amounts	0.1	0.1	0.0	0.0
Stock-based compensation expense	2.4	2.4	0.0	0.0
Common cash dividend declared	(44.7)	0.0	(44.7)	0.0
Equity, ending balance at Mar. 31, 2022	$ 3,441.1	$ 2,668.6	$ 974.5	$ (202.0)