Installment Receivables (Activity in the Deferred Interest and Allowance for Credit Losses for the Installment Receivables) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Deferred interest and allowance for credit losses, beginning of period	$ 506	$ 0	$ 329
Bad debt expense	61	93
Write-offs, net of recoveries	(28)	(105)
Change in deferred interest on short-term and long-term installment receivables	8	(43)
Derecognition of deferred interest and allowance for credit losses	(465)	274
Bad Debt Expense [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Bad debt expense	$ 322	$ 147	$ 398