Allowance for Credit Losses - Allowance for Credit Losses and Recorded Investment in Finance Receivables by Portfolio Segment (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2015
Allowance for Credit Losses for Finance Receivables:
Provisions		$ 128	$ 103	$ 278	$ 220
Transferred to held-for-sale	[1]	0	0	(7)	0
Finance Receivables:
Total Finance Receivables		66,383		66,383		$ 66,567
Retail Loan [Member]
Finance Receivables:
Total Finance Receivables		51,207		51,207		50,302
Finance Receivables, Net [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period		377	381	409	386
Charge-offs		(95)	(90)	(238)	(219)
Recoveries		10	16	37	47
Provisions		89	70	179	163
Transferred to held-for-sale				(6)
Allowance for credit losses at end of period		381	377	381	377
Ending balance: Individually evaluated for impairment		59	28	59	28
Ending balance: Collectively evaluated for impairment		322	349	322	349
Finance Receivables:
Total Finance Receivables		66,383	67,200	66,383	67,200	$ 66,567
Ending balance: Individually evaluated for impairment		502	209	502	209
Ending balance: Collectively evaluated for impairment		65,881	66,991	65,881	66,991
Finance Receivables, Net [Member] | Retail Loan [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period		263	299	299	296
Charge-offs		(95)	(89)	(237)	(217)
Recoveries		10	14	37	45
Provisions		80	72	159	172
Transferred to held-for-sale				0
Allowance for credit losses at end of period		258	296	258	296
Ending balance: Individually evaluated for impairment		0	0	0	0
Ending balance: Collectively evaluated for impairment		258	296	258	296
Finance Receivables:
Total Finance Receivables		51,207	50,637	51,207	50,637
Ending balance: Individually evaluated for impairment		0	0	0	0
Ending balance: Collectively evaluated for impairment		51,207	50,637	51,207	50,637
Finance Receivables, Net [Member] | Commercial Portfolio Segment
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period		0	1	2	2
Charge-offs		0	0	(1)	(1)
Recoveries		0	1	0	1
Provisions		0	0	1	0
Transferred to held-for-sale				(2)
Allowance for credit losses at end of period		0	2	0	2
Ending balance: Individually evaluated for impairment		0	0	0	0
Ending balance: Collectively evaluated for impairment		0	2	0	2
Finance Receivables:
Total Finance Receivables		0	503	0	503
Ending balance: Individually evaluated for impairment		0	0	0	0
Ending balance: Collectively evaluated for impairment		0	503	0	503
Finance Receivables, Net [Member] | Dealer Products [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period		114	81	108	88
Charge-offs		0	(1)	0	(1)
Recoveries		0	1	0	1
Provisions		9	(2)	19	(9)
Transferred to held-for-sale				(4)
Allowance for credit losses at end of period		123	79	123	79
Ending balance: Individually evaluated for impairment		59	28	59	28
Ending balance: Collectively evaluated for impairment		64	51	64	51
Finance Receivables:
Total Finance Receivables		15,176	16,060	15,176	16,060
Ending balance: Individually evaluated for impairment		502	209	502	209
Ending balance: Collectively evaluated for impairment		$ 14,674	$ 15,851	$ 14,674	$ 15,851

[1] Amount relates to the commercial finance business which was sold on October 1, 2015.