Installment Receivables (Schedule of Activity in Deferred Interest and Allowance for Credit Losses) (Details) - Financing Receivable [Member] - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred interest and allowance for credit losses, beginning of period	$ 506	$ 0
Bad debt expense	142	61
Write-offs, net of recoveries	(224)	(28)
Change in deferred interest on short-term and long-term installment receivables	(101)	8
Recognition of deferred interest and allowance for credit losses	0	465
Deferred interest and allowance for credit losses, end of period	$ 323	$ 506