Allowance for Credit Losses - Allowance for Credit Losses and Recorded Investment in Finance Receivables by Portfolio Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Mar. 31, 2016
Allowance for Credit Losses for Finance Receivables:
Provisions	$ 52	$ 45
Finance Receivables:
Total Finance Receivables	66,088		$ 66,262
Retail Loan [Member]
Finance Receivables:
Total Finance Receivables	50,148		50,363
Finance Receivables, Net [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period	421	409
Charge-offs	(82)	(61)
Recoveries	13	15
Provisions	14	32
Allowance for credit losses at end of period	366	395
Ending balance: Individually evaluated for impairment	30	60
Ending balance: Collectively evaluated for impairment	336	335
Finance Receivables:
Total Finance Receivables	66,088	67,055	$ 66,262
Ending balance: Individually evaluated for impairment	467	412
Ending balance: Collectively evaluated for impairment	65,621	66,643
Finance Receivables, Net [Member] | Retail Loan [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period	289	299
Charge-offs	(82)	(60)
Recoveries	13	15
Provisions	58	25
Allowance for credit losses at end of period	278	279
Ending balance: Individually evaluated for impairment	0	0
Ending balance: Collectively evaluated for impairment	278	279
Finance Receivables:
Total Finance Receivables	50,148	50,751
Ending balance: Individually evaluated for impairment	0	0
Ending balance: Collectively evaluated for impairment	50,148	50,751
Finance Receivables, Net [Member] | Dealer Products [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period	132	108
Charge-offs	0	0
Recoveries	0	0
Provisions	(44)	7
Allowance for credit losses at end of period	88	115
Ending balance: Individually evaluated for impairment	30	60
Ending balance: Collectively evaluated for impairment	58	55
Finance Receivables:
Total Finance Receivables	15,940	15,762
Ending balance: Individually evaluated for impairment	467	412
Ending balance: Collectively evaluated for impairment	$ 15,473	15,350
Finance Receivables, Net [Member] | Commercial Portfolio Segment [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period		2
Charge-offs		(1)
Recoveries		0
Provisions		0
Allowance for credit losses at end of period		1
Ending balance: Individually evaluated for impairment		0
Ending balance: Collectively evaluated for impairment		1
Finance Receivables:
Total Finance Receivables		542
Ending balance: Individually evaluated for impairment		0
Ending balance: Collectively evaluated for impairment		$ 542