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Acquisitions - Narrative (Details) - USD ($) $ in Millions	Jul. 31, 2019	Sep. 30, 2019	Mar. 31, 2019
Business Acquisition [Line Items]
Goodwill		$ 3,295	$ 3,179
Knight Point Systems, LLC
Business Acquisition [Line Items]
Purchase price	$ 265
Finite-lived Intangible Assets Acquired	125
Goodwill	116
Payments for acquisitions, net of cash acquired	250
Knight Point Systems, LLC \| Defense and Intelligence
Business Acquisition [Line Items]
Goodwill	22
Knight Point Systems, LLC \| Civilian and Health Care
Business Acquisition [Line Items]
Goodwill	$ 94
Minimum \| Knight Point Systems, LLC
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Maximum \| Knight Point Systems, LLC
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	12 years
Program assets \| Knight Point Systems, LLC
Business Acquisition [Line Items]
Finite-lived Intangible Assets Acquired	$ 102
Technology-Based Intangible Assets \| Knight Point Systems, LLC
Business Acquisition [Line Items]
Finite-lived Intangible Assets Acquired	$ 18
Technology-Based Intangible Assets \| Minimum \| Knight Point Systems, LLC
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years
Backlog \| Knight Point Systems, LLC
Business Acquisition [Line Items]
Finite-lived Intangible Assets Acquired	$ 5
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	1 year