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	116.4	0.0	116.4	0.0
Other comprehensive income (loss), net of tax expense	$ (496.7)	0.0	0.0	(496.7)
Stock repurchased and retired (in shares)	5,039,784
Common shares issued (in shares)	46,913,370
Non-vested common shares issued (in shares)	453,690
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	94,735
Stock Issued During Period, Value, Stock Options Exercised	$ 0.1	0.1	0.0	0.0
Common stock transactions:
Common shares purchased and retired	(198.9)	(198.9)	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	0.0	0.0	0.0	0.0
Stock-based compensation expense	$ 8.7	8.7	0.0	0.0
Common dividends (in dollars per share)	$ 1.23
Common cash dividend declared	$ (133.2)	0.0	(133.2)	0.0
Equity, ending balance at Sep. 30, 2022	3,005.5	2,477.4	1,035.8	(507.7)
Equity, beginning balance at Jun. 30, 2022	3,271.9	2,607.9	993.8	(329.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	85.7	0.0	85.7	0.0
Other comprehensive income (loss), net of tax expense	$ (177.9)	0.0	0.0	(177.9)
Stock repurchased and retired (in shares)	3,280,042
Non-vested common shares issued (in shares)	251
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	27,443
Common stock transactions:
Common shares purchased and retired	$ (133.0)	(133.0)	0.0	0.0
Non-vested common shares issued	0.0	0.0	0.0	0.0
Non-vested common shares forfeited or canceled	0.0	0.0	0.0	0.0
Stock-based compensation expense	$ 2.5	2.5	0.0	0.0
Common dividends (in dollars per share)	$ 0.41
Common cash dividend declared	$ (43.7)	0.0	(43.7)	0.0
Equity, ending balance at Sep. 30, 2022	3,005.5	2,477.4	1,035.8	(507.7)
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	196.0	0.0	196.0	0.0
Other comprehensive income (loss), net of tax expense	$ (44.6)	0.0	0.0	(44.6)
Stock repurchased and retired (in shares)	55,922
Non-vested common shares issued (in shares)	683,574
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	58,304
Common stock transactions:
Common shares purchased and retired	$ (1.9)	(1.9)	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	$ 8.6	8.6	0.0	0.0
Common dividends (in dollars per share)	$ 1.41
Common cash dividend declared	$ (146.4)	0.0	(146.4)	0.0
Equity, ending balance at Sep. 30, 2023	3,085.5	2,484.9	1,122.3	(521.7)
Equity, beginning balance at Jun. 30, 2023	3,121.1	2,481.3	1,098.8	(459.0)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	72.7	0.0	72.7	0.0
Other comprehensive income (loss), net of tax expense	$ (62.7)	0.0	0.0	(62.7)
Stock repurchased and retired (in shares)	494
Non-vested common shares issued (in shares)	12,663
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	21,481
Common stock transactions:
Common shares purchased and retired	$ 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	0.0	0.0	0.0	0.0
Stock-based compensation expense	$ 3.6	3.6	0.0	0.0
Common dividends (in dollars per share)	$ 0.47
Common cash dividend declared	$ (49.2)	0.0	(49.2)	0.0
Equity, ending balance at Sep. 30, 2023	$ 3,085.5	$ 2,484.9	$ 1,122.3	$ (521.7)