Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2026	Jun. 30, 2025
Disaggregation of Revenue [Line Items]
Revenue	$ 2,800	$ 2,924
Revenue from Contract with Customer Benchmark \| Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk (as a percent)	100.00%	100.00%
Revenue from Contract with Customer Benchmark \| Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk (as a percent)	100.00%	100.00%
Revenue from Contract with Customer Benchmark \| Contractor Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk (as a percent)	100.00%	100.00%
Prime Contractor
Disaggregation of Revenue [Line Items]
Revenue	$ 2,651	$ 2,741
Prime Contractor \| Revenue from Contract with Customer Benchmark \| Contractor Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk (as a percent)	95.00%	94.00%
Subcontractor
Disaggregation of Revenue [Line Items]
Revenue	$ 149	$ 183
Subcontractor \| Revenue from Contract with Customer Benchmark \| Contractor Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk (as a percent)	5.00%	6.00%
National Security
Disaggregation of Revenue [Line Items]
Revenue	$ 2,028	$ 2,001
National Security \| Revenue from Contract with Customer Benchmark \| Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk (as a percent)	72.00%	68.00%
Civil and Commercial
Disaggregation of Revenue [Line Items]
Revenue	$ 772	$ 923
Civil and Commercial \| Revenue from Contract with Customer Benchmark \| Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk (as a percent)	28.00%	32.00%
Cost-reimbursable
Disaggregation of Revenue [Line Items]
Revenue	$ 1,607	$ 1,758
Cost-reimbursable \| Revenue from Contract with Customer Benchmark \| Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk (as a percent)	57.00%	60.00%
Time-and-materials
Disaggregation of Revenue [Line Items]
Revenue	$ 616	$ 638
Time-and-materials \| Revenue from Contract with Customer Benchmark \| Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk (as a percent)	22.00%	22.00%
Fixed-price
Disaggregation of Revenue [Line Items]
Revenue	$ 577	$ 528
Fixed-price \| Revenue from Contract with Customer Benchmark \| Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk (as a percent)	21.00%	18.00%