Condensed Financial Information (Parent Company Only) - Condensed Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Condensed balance sheets:
Cash and cash equivalents	$ 870.5	$ 2,344.8
Investment in subsidiaries, at equity:
Other assets	348.7	184.1
Total assets	32,287.8	19,671.9
Long-term debt	98.9	98.7
Subordinated debentures held by subsidiary trusts		87.0
Total liabilities	29,214.0	17,685.3
Stockholders’ equity	3,073.8	1,986.6	$ 1,959.8	$ 2,013.9
Total liabilities and stockholders’ equity	32,287.8	19,671.9
Parent Company
Condensed balance sheets:
Cash and cash equivalents	154.8	181.1
Investment in subsidiaries, at equity:
Equity method investments	2,985.8	1,948.9
Advances from subsidiaries, net	0.1	5.9
Other assets	240.7	63.2
Total assets	3,381.4	2,199.1
Other liabilities	45.6	26.8
Subordinated debentures held by subsidiary trusts	163.1	87.0
Total liabilities	307.6	212.5
Stockholders’ equity	3,073.8	1,986.6
Total liabilities and stockholders’ equity	$ 3,381.4	$ 2,199.1