Acquisitions and Dispositions Acquisitions and Dispositions - Acquired Entities (Details)							3 Months Ended	12 Months Ended
	Sep. 30, 2019	Jun. 14, 2019	Jun. 12, 2019	Jan. 04, 2019 USD ($) employee vehicle branch	Dec. 04, 2018 USD ($)	Aug. 13, 2018 USD ($) employee branch vehicle	Dec. 31, 2020 USD ($) employee	Dec. 31, 2020 USD ($) employee acquisition	Dec. 31, 2019 USD ($) acquisition	Dec. 31, 2018 USD ($) acquisition	Sep. 30, 2020	Mar. 09, 2020	Nov. 01, 2018
Business Acquisition [Line Items]
Number of acquired operations | acquisition									4	1
G4S intercompany payments								$ (114,500,000)	$ 35,000,000.0	$ 69,000,000.0
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Indemnification asset							$ (17,500,000)	(17,500,000)	(20,600,000)
Restricted cash							322,000,000.0	322,000,000.0	158,000,000.0
Right-of-use assets, net							322,000,000.0	322,000,000.0	270,300,000
Goodwill							$ 1,219,200,000	1,219,200,000	784,600,000	$ 678,600,000
G4Si
Business Acquisition [Line Items]
Percentage of shares acquired												100.00%
G4S
Business Acquisition [Line Items]
Percentage of shares acquired											100.00%
G4S intercompany payments								$ 111,000,000
Percentage of Total Purchase Price							90.00%	90.00%
Annual revenues								$ 740,000,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid								686,500,000
Contingent consideration							$ 22,000,000.0	22,000,000.0
Liabilities assumed from seller								1,600,000
Receivable from seller								(400,000)
Fair value of purchase consideration								709,700,000
Cash							218,200,000	218,200,000
Restricted cash							30,100,000	30,100,000
Accounts receivables							135,200,000	135,200,000
Other current assets							24,900,000	24,900,000
Property and Equipment, net							119,700,000	119,700,000
Right-of-use assets, net							66,500,000	66,500,000
Intangible assets							175,900,000	175,900,000
Goodwill							422,500,000	422,500,000
Other noncurrent assets							18,200,000	18,200,000
Current liabilities							(281,000,000.0)	(281,000,000.0)
Lease liability							(61,300,000)	(61,300,000)
Noncurrent liabilities							(95,000,000.0)	(95,000,000.0)
Fair value of net assets acquired							773,900,000	773,900,000
Fair value of noncontrolling interest							(64,200,000)	(64,200,000)
G4S | MEA & GS
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill							70,000,000	70,000,000
G4S | Europe
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill							190,000,000	190,000,000
G4S | Asia Pacific Member
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill							160,000,000	160,000,000
G4S | South America Member
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill							3,000,000	$ 3,000,000
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%
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				$ 135,700,000
Indemnification asset				(1,900,000)
Fair value of purchase consideration				133,800,000
Cash				1,400,000
Accounts receivables				8,900,000
Other current assets				500,000
Property and Equipment, net				2,400,000
Intangible assets				49,000,000.0
Goodwill				85,100,000
Other noncurrent assets				5,800,000
Current liabilities				(11,400,000)
Noncurrent liabilities				(7,900,000)
Fair value of net assets acquired				133,800,000
Dunbar
Business Acquisition [Line Items]
Acquisition date						Aug. 13, 2018
Percentage of shares acquired						100.00%
Entity Number of Employees | employee						5,400
Entity Number Of Branches | branch						78
Entity Number Of Armored Vehicles | vehicle						1,600
Intangible asset decrease									20,000,000
Goodwill increase									21,000,000
Noncurrent assets increase									11,000,000
Noncurrent liability increase									$ 16,000,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid						$ 540,500,000
Receivable from seller							$ 6,000,000
Fair value of purchase consideration						540,500,000
Cash						25,800,000
Accounts receivables						31,900,000
Other current assets						11,700,000
Property and Equipment, net						56,600,000
Intangible assets						162,000,000.0
Goodwill						304,100,000
Other noncurrent assets						21,100,000
Current liabilities						(29,500,000)
Noncurrent liabilities						(43,200,000)
Fair value of net assets acquired						540,500,000
Other Acquisitions
Business Acquisition [Line Items]
Number of acquired operations | acquisition								3
Entity Number of Employees | employee							1,300	1,300
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid								$ 60,600,000
Contingent consideration							$ 1,600,000	1,600,000
Indemnification asset							(13,300,000)	(13,300,000)
Fair value of purchase consideration								48,900,000
Cash							6,500,000	6,500,000
Accounts receivables							4,500,000	4,500,000
Property and Equipment, net							7,100,000	7,100,000
Intangible assets							24,300,000	24,300,000
Goodwill							34,300,000	34,300,000
Other noncurrent assets							2,000,000.0	2,000,000.0
Current liabilities							(15,200,000)	(15,200,000)
Noncurrent liabilities							(14,600,000)	(14,600,000)
Fair value of net assets acquired							48,900,000	$ 48,900,000
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%
Worldbridge
Business Acquisition [Line Items]
Acquisition date					Dec. 04, 2018
Percentage of shares acquired					60.00%
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Fair value of purchase consideration					$ 2,000,000
Brink's de Colombia SA
Business Acquisition [Line Items]
Percentage of shares acquired													42.00%
Ownership percentage after remaining noncontrolling interest 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							$ 176,000,000	$ 176,000,000
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				47,000,000
Customer relationships | Dunbar
Business Acquisition [Line Items]
Remaining Amortization Period									15 years
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Intangible assets						148,000,000
Finite-lived 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				1,000,000
Finite-lived trade names | Dunbar
Business Acquisition [Line Items]
Remaining Amortization Period									8 years
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Intangible assets						$ 14,000,000
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				$ 1,000,000