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, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2016
Allowance for Credit Losses for Finance Receivables:
Provisions		$ 183	$ 128	$ 396	$ 278
Transferred to held-for-sale	[1]	0	0	0	(7)
Finance Receivables:
Total Finance Receivables		68,789		68,789		$ 66,262
Retail Loan [Member]
Finance Receivables:
Total Finance Receivables		51,570		51,570		50,363
Finance Receivables, Net [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period		389	377	421	409
Charge-offs		(113)	(95)	(294)	(238)
Recoveries		12	10	38	37
Provisions		133	89	256	179
Transferred to held-for-sale					(6)
Allowance for credit losses at end of period		421	381	421	381
Ending balance: Individually evaluated for impairment		26	59	26	59
Ending balance: Collectively evaluated for impairment		395	322	395	322
Finance Receivables:
Total Finance Receivables		68,789	66,383	68,789	66,383	$ 66,262
Ending balance: Individually evaluated for impairment		438	502	438	502
Ending balance: Collectively evaluated for impairment		68,351	65,881	68,351	65,881
Finance Receivables, Net [Member] | Retail Loan [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period		295	263	289	299
Charge-offs		(113)	(95)	(294)	(237)
Recoveries		12	10	38	37
Provisions		120	80	281	159
Transferred to held-for-sale					0
Allowance for credit losses at end of period		314	258	314	258
Ending balance: Individually evaluated for impairment		0	0	0	0
Ending balance: Collectively evaluated for impairment		314	258	314	258
Finance Receivables:
Total Finance Receivables		51,570	51,207	51,570	51,207
Ending balance: Individually evaluated for impairment		0	0	0	0
Ending balance: Collectively evaluated for impairment		51,570	51,207	51,570	51,207
Finance Receivables, Net [Member] | Dealer Products [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period		94	114	132	108
Charge-offs		0	0	0	0
Recoveries		0	0	0	0
Provisions		13	9	(25)	19
Transferred to held-for-sale					(4)
Allowance for credit losses at end of period		107	123	107	123
Ending balance: Individually evaluated for impairment		26	59	26	59
Ending balance: Collectively evaluated for impairment		81	64	81	64
Finance Receivables:
Total Finance Receivables		17,219	15,176	17,219	15,176
Ending balance: Individually evaluated for impairment		438	502	438	502
Ending balance: Collectively evaluated for impairment		$ 16,781	14,674	$ 16,781	14,674
Finance Receivables, Net [Member] | Commercial Portfolio Segment [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period			0		2
Charge-offs			0		(1)
Recoveries			0		0
Provisions			0		1
Transferred to held-for-sale					(2)
Allowance for credit losses at end of period			0		0
Ending balance: Individually evaluated for impairment			0		0
Ending balance: Collectively evaluated for impairment			0		0
Finance Receivables:
Total Finance Receivables			0		0
Ending balance: Individually evaluated for impairment			0		0
Ending balance: Collectively evaluated for impairment			$ 0		$ 0

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