Accounts Receivable (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	$ 974	$ 927
Unbilled
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	424	346
Trade & Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	550	581
Operating Segments | Subtotal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	974	927
Operating Segments | Subtotal | Unbilled
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	424	346
Operating Segments | Subtotal | Trade & Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	550	581
Operating Segments | Government Solutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	650	600
Operating Segments | Government Solutions | Unbilled
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	318	266
Operating Segments | Government Solutions | Trade & Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	332	334
Operating Segments | Technology Solutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	73	73
Operating Segments | Technology Solutions | Unbilled
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	22	11
Operating Segments | Technology Solutions | Trade & Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	51	62
Operating Segments | Energy Solutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	251	254
Operating Segments | Energy Solutions | Unbilled
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	84	69
Operating Segments | Energy Solutions | Trade & Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	167	185
Operating Segments | Non-strategic Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	0	0
Operating Segments | Non-strategic Business | Unbilled
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	0	0
Operating Segments | Non-strategic Business | Trade & Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net of allowance for doubtful accounts	$ 0	$ 0