Acquisitions and Dispositions - Acquired Entities (Details) $ in Millions							6 Months Ended
	Apr. 01, 2020	Mar. 09, 2020 USD ($)	Sep. 30, 2019	Jun. 14, 2019	Jun. 12, 2019	Jan. 04, 2019 USD ($) employee vehicle branch	Jun. 30, 2020 USD ($) employee acquisition	Dec. 31, 2019 USD ($)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Restricted cash							$ 171.5	$ 158.0
Right-of-use assets, net							329.8	270.3
Goodwill							1,114.0	$ 784.6
Fair value of noncontrolling interest							$ (67.8)
G4Si
Business Acquisition [Line Items]
Acquisition date		Mar. 09, 2020
Percentage of shares acquired		100.00%
G4S
Business Acquisition [Line Items]
Acquisition date	Apr. 01, 2020
Percentage of shares acquired							100.00%
Percentage of total purchase price							80.00%
Annual revenues		$ 690.0
Goodwill not allocated							$ 12.0
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid							651.2
Contingent consideration							38.0
Liabilities assumed from seller							9.4
Receivable from seller							(3.9)
Fair value of purchase consideration		$ 694.7					694.7
Cash							214.3
Restricted cash							30.1
Accounts receivable							129.5
Other current assets							22.6
Property and equipment, net							123.1
Right-of-use assets, net							72.0
Intangible assets							157.7
Goodwill							370.3
Other noncurrent assets							19.3
Current liabilities							(229.8)
Lease liabilities							(58.2)
Noncurrent liabilities							(88.4)
Fair value of net assets acquired							$ 762.5
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							$ 60.2
Contingent consideration							1.6
Indemnification asset							(12.9)
Fair value of purchase consideration							48.9
Cash							6.5
Accounts receivable							4.5
Property and equipment, net							7.1
Intangible assets							24.4
Goodwill							33.8
Other noncurrent assets							1.9
Current liabilities							(15.2)
Noncurrent liabilities							(14.1)
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							$ 158.0
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							$ 257.0
Asia Pacific | G4S
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill							97.0
South America | G4S
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill							$ 5.0