Condensed Financial Information (Parent Company Only) - Condensed Statements of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Condensed Financial Statements, Captions
Salaries and benefits	$ 274.6	$ 270.9	$ 263.1
Interest expense	352.6	480.9	401.3
Income before income tax	391.7	294.5	336.8
Income tax benefit	89.6	68.5	79.3
Net income	302.1	226.0	257.5
Parent Company
Condensed Financial Statements, Captions
Dividends from subsidiaries	369.4	205.0	360.0
Other interest income	0.4	0.4	0.5
Other income, primarily management fees from subsidiaries	42.1	54.3	51.6
Total income	411.9	259.7	412.1
Salaries and benefits	31.8	43.6	34.5
Interest expense	21.3	18.6	18.4
Other operating expenses, net	29.1	27.8	22.5
Total expenses	82.2	90.0	75.4
Income before income tax	329.7	169.7	336.7
Income tax benefit	(9.1)	(7.2)	(4.2)
Income before undistributed earnings of subsidiaries	338.8	176.9	340.9
Undistributed (loss) earnings of subsidiaries	(36.7)	49.1	(83.4)
Net income	$ 302.1	$ 226.0	$ 257.5