Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Accounts and accrued income receivable, allowances	$ 21.8	$ 21.3
Pledged securities included in debt securities	107.0	86.0
Debt securities, amortized cost	$ 7,895.2	$ 9,169.6
Preferred stock, par value	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	0.5	0.5
Preferred stock, outstanding	0.0	0.0
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	300.0	300.0
Common stock, shares outstanding	103.1	103.2