Installment Receivables (Activity in the Deferred Interest and Allowance for Credit Losses for the Installment Receivables) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2015	Mar. 31, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Deferred interest and allowance for credit losses, beginning of period	$ 329	$ 124
Bad debt expense	93	398
Write-offs, net of recoveries	(105)	(255)
Change in deferred interest on short-term and long-term installment receivables	(43)	62
Derecognized allowances and deferred interest	(274)	0
Deferred interest and allowance for credit losses, end of period	$ 0	$ 329