Operating Information by Segment and Geographic Area - External Revenue and Segment Profit (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment reporting information
Revenue	$ 15,474	$ 13,744	$ 14,156
Segment profit (loss)	147	209	(273)
G&A	(232)	(237)	(226)
Impairment	0	24	(290)
Gain (loss) on pension settlement	0	42	(198)
Foreign currency gain (loss)	(98)	25	(13)
Interest income (expense), net	168	35	(73)
Earnings (loss) from Cont Ops attributable to NCI	(60)	(72)	39
Earnings (loss) from Cont Ops before taxes	315	244	$ (346)
Total assets	6,973	6,827
Goodwill	$ 206	$ 206
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Earnings (loss) from Cont Ops before taxes	Earnings (loss) from Cont Ops before taxes	Earnings (loss) from Cont Ops before taxes
Continuing Operations
Segment reporting information
Depreciation (all but Corporate included in segment profit)	$ 74	$ 73	$ 73
Capital expenditures	106	75	66
Reportable segments
Segment reporting information
Goodwill	206	206
Reportable segments | Continuing Operations
Segment reporting information
Revenue	15,474	13,744	14,156
Segment profit (loss)	537	427	415
Intercompany revenue for our professional staffing business, excluded from revenue above | Continuing Operations
Segment reporting information
Revenue	299	249	269
Energy Solutions | Reportable segments
Segment reporting information
Total assets	1,053	967
Goodwill	13	13
Energy Solutions | Reportable segments | Continuing Operations
Segment reporting information
Revenue	6,307	5,872	4,956
Segment profit (loss)	381	301	250
Depreciation (all but Corporate included in segment profit)	0	0	0
Capital expenditures	0	0	0
Urban Solutions | Reportable segments
Segment reporting information
Total assets	1,211	1,170
Goodwill	129	129
Urban Solutions | Reportable segments | Continuing Operations
Segment reporting information
Revenue	5,262	4,373	4,832
Segment profit (loss)	268	17	41
Depreciation (all but Corporate included in segment profit)	10	9	9
Capital expenditures	20	14	25
Mission Solutions | Reportable segments
Segment reporting information
Total assets	577	485
Goodwill	58	58
Mission Solutions | Reportable segments | Continuing Operations
Segment reporting information
Revenue	2,655	2,289	3,063
Segment profit (loss)	116	136	155
Depreciation (all but Corporate included in segment profit)	3	3	4
Capital expenditures	4	4	3
Other | Reportable segments
Segment reporting information
Total assets	509	583
Goodwill	6	6
Other | Reportable segments | Continuing Operations
Segment reporting information
Revenue	1,250	1,210	1,305
Segment profit (loss)	(228)	(27)	(31)
Depreciation (all but Corporate included in segment profit)	19	18	7
Capital expenditures	15	21	19
Corporate | Reportable segments
Segment reporting information
Total assets	3,623	3,622
Corporate | Reportable segments | Continuing Operations
Segment reporting information
Depreciation (all but Corporate included in segment profit)	42	43	53
Capital expenditures	$ 67	$ 36	$ 19