Goodwill and Identifiable Assets (Acquired Intangible Assets) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Intangible assets subject to amortization:
Gross Carrying Amount	$ 547.2	$ 524.7
Accumulated Amortization	319.0	307.1
Net Carrying Amount	228.2	217.6
Intangible assets not subject to amortization:
Trademarks, Carrying Amount	258.9	258.9
Intangible Assets, Gross (Excluding Goodwill)	806.1	783.6
Intangible Assets, Net (Excluding Goodwill)	487.1	476.5
Customer and Contractual Relationships
Intangible assets subject to amortization:
Gross Carrying Amount	403.4	384.9
Accumulated Amortization	189.9	179.9
Net Carrying Amount	$ 213.5	205.0
Customer and Contractual Relationships | Minimum [Member]
Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 months
Customer and Contractual Relationships | Maximum [Member]
Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	12 years 9 months
Contractor Relations
Intangible assets subject to amortization:
Gross Carrying Amount	$ 71.0	71.1
Accumulated Amortization	70.6	70.6
Net Carrying Amount	$ 0.4	0.5
Contractor Relations | Minimum [Member]
Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 years
Contractor Relations | Maximum [Member]
Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Backlog
Intangible assets subject to amortization:
Gross Carrying Amount	$ 28.3	25.0
Accumulated Amortization	24.8	23.9
Net Carrying Amount	$ 3.5	1.1
Backlog | Minimum [Member]
Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	1 year
Backlog | Maximum [Member]
Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 years 9 months
Noncompete Agreements
Intangible assets subject to amortization:
Gross Carrying Amount	$ 25.6	24.8
Accumulated Amortization	14.8	13.8
Net Carrying Amount	$ 10.8	11.0
Noncompete Agreements | Minimum [Member]
Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 years
Noncompete Agreements | Maximum [Member]
Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	7 years
In-use software
Intangible assets subject to amortization:
Gross Carrying Amount	$ 18.9	18.9
Accumulated Amortization	18.9	18.9
Net Carrying Amount	$ 0.0	$ 0.0
In-use software | Minimum [Member]
Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	6 years