Acquisitions and Dispositions - Acquired Entities (Details) $ in Millions						9 Months Ended
	Mar. 09, 2020	Sep. 30, 2019	Jun. 14, 2019	Jun. 12, 2019	Jan. 04, 2019 USD ($) employee vehicle branch	Sep. 30, 2020 USD ($) employee acquisition	Dec. 31, 2019 USD ($)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Restricted cash						$ 203.0	$ 158.0
Right-of-use assets, net						325.9	270.3
Goodwill						1,184.4	$ 784.6
Fair value of noncontrolling interest						$ (67.7)
G4Si
Business Acquisition [Line Items]
Acquisition date	Mar. 09, 2020
Percentage of shares acquired	100.00%
G4S
Business Acquisition [Line Items]
Percentage of shares acquired						100.00%
Percentage of total purchase price						90.00%
Annual revenues						$ 740.0
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid						672.3
Contingent consideration						38.0
Liabilities assumed from seller						12.2
Receivable from seller						(2.8)
Fair value of purchase consideration						719.7
Cash						218.8
Restricted cash						30.1
Accounts receivable						136.8
Other current assets						25.5
Property and equipment, net						123.4
Right-of-use assets, net						73.7
Intangible assets						175.0
Goodwill						424.0
Other noncurrent assets						19.3
Current liabilities						(286.3)
Lease liabilities						(59.5)
Noncurrent liabilities						(93.4)
Fair value of net assets acquired						$ 787.4
G4S Tranche III
Business Acquisition [Line Items]
Percentage of shares acquired						100.00%
Rodoban
Business Acquisition [Line Items]
Acquisition date					Jan. 04, 2019
Percentage of shares acquired					100.00%
Annual revenues					$ 80.0
Entity number of employees | employee					2,900
Entity Number of branches | branch					13
Entity Number of armored vehicles | vehicle					190
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid					$ 135.7
Indemnification asset					(1.9)
Fair value of purchase consideration					133.8
Cash					1.4
Accounts receivable					8.9
Other current assets					0.5
Property and equipment, net					2.4
Intangible assets					49.0
Goodwill					85.1
Other noncurrent assets					5.8
Current liabilities					(11.4)
Noncurrent liabilities					(7.9)
Fair value of net assets acquired					133.8
Other Acquisitions
Business Acquisition [Line Items]
Entity number of employees | employee						1,300
Number of Businesses Acquired | acquisition						3
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid						$ 60.6
Contingent consideration						1.6
Indemnification asset						(13.3)
Fair value of purchase consideration						48.9
Cash						6.5
Accounts receivable						4.5
Property and equipment, net						7.1
Intangible assets						24.3
Goodwill						34.3
Other noncurrent assets						2.0
Current liabilities						(15.2)
Noncurrent liabilities						(14.6)
Fair value of net assets acquired						$ 48.9
BI
Business Acquisition [Line Items]
Acquisition date				Jun. 12, 2019
Percentage of shares acquired				100.00%
COMEF
Business Acquisition [Line Items]
Acquisition date			Jun. 14, 2019
Percentage of shares acquired			100.00%
TVS
Business Acquisition [Line Items]
Acquisition date		Sep. 30, 2019
Percentage of shares acquired		100.00%
Customer relationships | G4S
Business Acquisition [Line Items]
Remaining Amortization Period						15 years
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Intangible assets						$ 175.0
Customer relationships | Rodoban
Business Acquisition [Line Items]
Remaining Amortization Period						11 years
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Intangible assets					47.0
Trade names | Rodoban
Business Acquisition [Line Items]
Remaining Amortization Period						1 year
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Intangible assets					1.0
Noncompete agreements | Rodoban
Business Acquisition [Line Items]
Remaining Amortization Period						5 years
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Intangible assets					$ 1.0
EMEA | G4S
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill						$ 255.0
Asia Pacific | G4S
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill						165.0
South America | G4S
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill						$ 4.0