Consolidated Statement of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	Common stock	Retained earnings	Accumulated other comprehensive loss
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 income	(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	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	0.1	(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)
Equity, beginning balance at Dec. 31, 2022	3,073.8	2,478.2	1,072.7	(477.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	56.3	0.0	56.3	0.0
Other comprehensive income (loss), net of tax expense	78.0	0.0	0.0	78.0
Common stock transactions:
Common shares purchased and retired	(1.8)	(1.8)	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-based compensation expense	2.3	2.3	0.0	0.0
Common cash dividend declared	(48.3)	0.0	(48.3)	0.0
Equity, ending balance at Mar. 31, 2023	$ 3,160.3	$ 2,478.7	$ 1,080.7	$ (399.1)