Goodwill and Identifiable Assets (Goodwill) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Goodwill [Roll Forward]
Beginning balance	$ 1,894.1	$ 1,891.9
Purchase price adjustment		1.1
Translation adjustment	(0.4)	1.1
Ending balance	1,893.7	1,894.1
Commercial
Goodwill [Roll Forward]
Beginning balance	1,075.8	1,074.7
Purchase price adjustment		0.0
Translation adjustment	(0.4)	1.1
Ending balance	1,075.4	1,075.8
Federal Government
Goodwill [Roll Forward]
Beginning balance	818.3	817.2
Purchase price adjustment		1.1
Translation adjustment	0.0	0.0
Ending balance	$ 818.3	$ 818.3