Receivables - Receivables, Net of Allowance (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables, net of allowance for doubtful accounts	$ 5,181	$ 5,481
Billed trade receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables, net of allowance for doubtful accounts	2,508	3,110
Unbilled receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables, net of allowance for doubtful accounts	1,114	1,273
Other receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables, net of allowance for doubtful accounts	$ 1,559	$ 1,098