Schedule I - Condensed Financial Information of the Registrant - Condensed Statements of Income and Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CONDENSED STATEMENTS OF INCOME/(LOSS) AND COMPREHENSIVE INCOME/(LOSS)
Revenues		$ 5,070.8	$ 4,835.0	$ 5,292.1
Expenses	[1]	3,947.7	3,867.7	4,358.1
Operating income		1,123.1	967.3	934.0
Gain on divestitures of businesses (Note 5)				524.6
Gain on sale of noncontrolling interest in private company		47.9
Interest income		1.4	3.2	6.3
Interest expense		(105.5)	(118.5)	(152.0)
Other income/(expense), net		(21.7)	3.1	8.5
Income tax (expense)/benefit		(129.6)	(110.8)	(263.1)
Net income		805.8	744.3	1,058.3
Other comprehensive income, net of tax		107.4	49.5	22.0
Comprehensive income		913.2	793.8	1,080.3
Parent Company | Reportable Legal Entities
CONDENSED STATEMENTS OF INCOME/(LOSS) AND COMPREHENSIVE INCOME/(LOSS)
Gain on divestitures of businesses (Note 5)				524.6
Gain on sale of noncontrolling interest in private company		47.9
Interest expense		(115.9)	(158.5)	(181.5)
Other income/(expense), net		(14.7)	3.6	2.7
Income/(loss) before equity earnings/(losses) of affiliates and income taxes		(82.7)	(154.9)	345.8
Equity in earnings of affiliates, net of tax		869.1	861.7	827.3
Income tax (expense)/benefit		19.4	37.5	(114.8)
Net income		805.8	744.3	1,058.3
Other comprehensive income, net of tax		2.5	0.4	0.2
Other comprehensive income of affiliates, net of tax		104.9	49.1	21.8
Comprehensive income		$ 913.2	$ 793.8	$ 1,080.3

[1] As further described in Note 7, total expenses include amounts incurred with related parties of $54.7 million, $54.6 million, and $57.1 million for the years ended December 31, 2021, 2020, and 2019, respectively.