SEGMENT INFORMATION - Reportable Segment Revenue, Income (Loss) Before Income Taxes, (Provision) Benefit for Income Taxes and Net Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information
Total revenues	$ 4,705.1	$ 4,163.4	$ 13,393.7	$ 12,153.1
Income before income taxes	220.5	257.2	654.8	779.6
U.S.
Segment Reporting Information
Total revenues	3,899.7	3,484.3	11,041.7	10,012.8
Income before income taxes	203.1	231.5	591.6	703.8
U.K.
Segment Reporting Information
Total revenues	805.5	679.1	2,352.0	2,140.3
Income before income taxes	$ 17.4	$ 25.7	$ 63.2	$ 75.9