Revenue - Summary of Disaggregated Revenue (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Net revenues	$ 958	$ 1,118	$ 2,705	$ 3,107
United States [Member]
Disaggregation of Revenue [Line Items]
Net revenues	901	1,050	2,557	2,883
Canada and United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Net revenues	57	68	148	224
Life Safety [Member]
Disaggregation of Revenue [Line Items]
Net revenues	322	363	963	1,038
Mechanical [Member]
Disaggregation of Revenue [Line Items]
Net revenues	82	109	236	304
Infrastructure/Utility [Member]
Disaggregation of Revenue [Line Items]
Net revenues	230	241	615	645
Fabrication [Member]
Disaggregation of Revenue [Line Items]
Net revenues	58	44	129	114
Specialty Contracting [Member]
Disaggregation of Revenue [Line Items]
Net revenues	112	122	305	348
Transmission [Member]
Disaggregation of Revenue [Line Items]
Net revenues	127	156	336	443
Civil [Member]
Disaggregation of Revenue [Line Items]
Net revenues	25	29	50	45
Inspection [Member]
Disaggregation of Revenue [Line Items]
Net revenues	6	60	82	182
Corporate and Eliminations [Member]
Disaggregation of Revenue [Line Items]
Net revenues	(4)	(6)	(11)	(12)
Safety Services [Member]
Disaggregation of Revenue [Line Items]
Net revenues	404	472	1,199	1,342
Safety Services [Member] \| United States [Member]
Disaggregation of Revenue [Line Items]
Net revenues	361	416	1,074	1,185
Safety Services [Member] \| Canada and United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Net revenues	43	56	125	157
Safety Services [Member] \| Life Safety [Member]
Disaggregation of Revenue [Line Items]
Net revenues	322	363	963	1,038
Safety Services [Member] \| Mechanical [Member]
Disaggregation of Revenue [Line Items]
Net revenues	82	109	236	304
Specialty Services [Member]
Disaggregation of Revenue [Line Items]
Net revenues	400	407	1,049	1,107
Specialty Services [Member] \| United States [Member]
Disaggregation of Revenue [Line Items]
Net revenues	400	407	1,049	1,107
Specialty Services [Member] \| Infrastructure/Utility [Member]
Disaggregation of Revenue [Line Items]
Net revenues	230	241	615	645
Specialty Services [Member] \| Fabrication [Member]
Disaggregation of Revenue [Line Items]
Net revenues	58	44	129	114
Specialty Services [Member] \| Specialty Contracting [Member]
Disaggregation of Revenue [Line Items]
Net revenues	112	122	305	348
Industrial Services [Member]
Disaggregation of Revenue [Line Items]
Net revenues	158	245	468	670
Industrial Services [Member] \| United States [Member]
Disaggregation of Revenue [Line Items]
Net revenues	144	233	445	603
Industrial Services [Member] \| Canada and United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Net revenues	14	12	23	67
Industrial Services [Member] \| Transmission [Member]
Disaggregation of Revenue [Line Items]
Net revenues	127	156	336	443
Industrial Services [Member] \| Civil [Member]
Disaggregation of Revenue [Line Items]
Net revenues	25	29	50	45
Industrial Services [Member] \| Inspection [Member]
Disaggregation of Revenue [Line Items]
Net revenues	6	60	82	182
Corporate and Eliminations [Member]
Disaggregation of Revenue [Line Items]
Net revenues	(4)	(6)	(11)	(12)
Corporate and Eliminations [Member] \| United States [Member]
Disaggregation of Revenue [Line Items]
Net revenues	(4)	(6)	(11)	(12)
Corporate and Eliminations [Member] \| Corporate and Eliminations [Member]
Disaggregation of Revenue [Line Items]
Net revenues	$ (4)	$ (6)	$ (11)	$ (12)