Installment Receivables (Schedule of Activity in Deferred Interest and Allowance for Credit Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred interest and allowance for credit losses, beginning of period	$ 323	$ 506
Bad debt expense	116	142
Write-offs, net of recoveries	(118)	(224)
Change in deferred interest on short-term and long-term installment receivables	15	(101)
Deferred interest and allowance for credit losses, end of period	286	323
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Change in deferred interest on short-term and long-term installment receivables	$ (50)	$ 0