Allowance for Credit Losses - Allowance for Credit Losses for Finance Receivables and Finance Receivables by Portfolio Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2017
Allowance for Credit Losses for Finance Receivables:
Provisions	$ 85	$ 52
Finance Receivables:
Total Finance Receivables	69,650		$ 69,308
Retail Loan [Member]
Finance Receivables:
Total Finance Receivables	51,375		51,409
Finance Receivables, Net [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period	467	421
Charge-offs	(79)	(82)
Recoveries	13	13
Provisions	52	14
Allowance for credit losses at end of period	453	366
Allowance for Credit Losses:
Ending balance: Individually evaluated for impairment	47	30
Ending balance: Collectively evaluated for impairment	406	336
Finance Receivables:
Total Finance Receivables	69,650	66,088	$ 69,308
Ending balance: Individually evaluated for impairment	494	467
Ending balance: Collectively evaluated for impairment	69,156	65,621
Finance Receivables, Net [Member] | Retail Loan [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period	344	289
Charge-offs	(79)	(82)
Recoveries	13	13
Provisions	44	58
Allowance for credit losses at end of period	322	278
Allowance for Credit Losses:
Ending balance: Individually evaluated for impairment	0	0
Ending balance: Collectively evaluated for impairment	322	278
Finance Receivables:
Total Finance Receivables	51,375	50,148
Ending balance: Individually evaluated for impairment	0	0
Ending balance: Collectively evaluated for impairment	51,375	50,148
Finance Receivables, Net [Member] | Dealer Products [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period	123	132
Charge-offs	0	0
Recoveries	0	0
Provisions	8	(44)
Allowance for credit losses at end of period	131	88
Allowance for Credit Losses:
Ending balance: Individually evaluated for impairment	47	30
Ending balance: Collectively evaluated for impairment	84	58
Finance Receivables:
Total Finance Receivables	18,275	15,940
Ending balance: Individually evaluated for impairment	494	467
Ending balance: Collectively evaluated for impairment	$ 17,781	$ 15,473