The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Goodwill and Identifiable Assets Goodwill (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Goodwill [Roll Forward]
Gross goodwill, period start	$ 1,894.1	$ 1,891.9	$ 1,894.1	$ 1,891.9
Purchase price adjustment				1.1
Translation adjustment	1.1		(1.0)
Gross goodwill, period end			1,893.1	1,894.1	$ 1,891.9
Amortization of intangible assets			58.1	71.7	65.1
Commercial Business
Goodwill [Roll Forward]
Gross goodwill, period start	1,075.8	1,074.7	1,075.8	1,074.7
Purchase price adjustment				0.0
Translation adjustment		1.1	(1.0)
Gross goodwill, period end			1,074.8	1,075.8	1,074.7
Federal Government Business
Goodwill [Roll Forward]
Gross goodwill, period start	$ 818.3	817.2	818.3	817.2
Purchase price adjustment		1.1
Translation adjustment		$ 0.0	0.0
Gross goodwill, period end			$ 818.3	$ 818.3	$ 817.2