Installment Receivables - Schedule of Activity in the Deferred Interest Allowance for Credit Losses (Details) - Financing Receivable - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Deferred interest and allowance for credit losses, beginning of period	$ 506	$ 0
Bad debt expense	135	61
Write-offs, net of recoveries	(177)	(28)
Change in deferred interest on short-term and long-term installment receivables	(74)	8
Recognition of deferred interest and allowance for credit losses	0	465
Deferred interest and allowance for credit losses, end of period	$ 390	$ 506