Condensed Financial Information (Parent Company Only) - Condensed Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Condensed balance sheets:
Cash and cash equivalents	$ 1,309.7	$ 896.6
Investment in subsidiaries, at equity:
Other assets	238.1	304.0
Assets	26,640.6	29,137.4
Subordinated debentures held by subsidiary trusts	149.8	163.1
Total liabilities	23,193.6	25,833.4
Stockholders’ equity	3,447.0	3,304.0	$ 3,227.5	$ 3,073.8
Total liabilities and stockholders’ equity	26,640.6	29,137.4
Parent Company
Condensed balance sheets:
Cash and cash equivalents	308.3	273.4
Investment in subsidiaries, at equity:
Equity method investments	3,312.1	3,160.5
Advances from subsidiaries, net	105.9	46.8
Other assets	131.4	137.9
Assets	3,857.7	3,618.6
Other liabilities	138.6	52.4
Long-term debt	122.3	99.1
Subordinated debentures held by subsidiary trusts	149.8	163.1
Total liabilities	410.7	314.6
Stockholders’ equity	3,447.0	3,304.0
Total liabilities and stockholders’ equity	$ 3,857.7	$ 3,618.6