Allowance for Credit Losses - Allowance for Credit Losses and Recorded Investment in Finance Receivables by Portfolio Segment (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Allowance for Credit Losses for Finance Receivables:
Provisions		$ 163	$ 128	$ 105	$ 45	$ 88	$ 103	$ 79	$ 38	$ 441	$ 308	$ 170
Transferred to held-for-sale	[1]									(7)	0	0
Finance Receivables:
Total Finance Receivables		66,262				66,567				66,262	66,567
Retail Loan [Member]
Finance Receivables:
Total Finance Receivables		50,363				50,302				50,363	50,302
Finance Receivables, Net [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period					409				386	409	386
Charge-offs										(329)	(276)
Recoveries										49	63
Provisions										298	236
Transferred to held-for-sale										(6)
Allowance for credit losses at end of period		421				409				421	409	386
Ending balance: Individually evaluated for impairment		54				55				54	55
Ending balance: Collectively evaluated for impairment		367				354				367	354
Finance Receivables:
Total Finance Receivables		66,262				66,567				66,262	66,567
Ending balance: Individually evaluated for impairment		540				360				540	360
Ending balance: Collectively evaluated for impairment		65,722				66,207				65,722	66,207
Finance Receivables, Net [Member] | Retail Loan [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period					299				296	299	296
Charge-offs										(328)	(273)
Recoveries										49	61
Provisions										269	215
Transferred to held-for-sale										0
Allowance for credit losses at end of period		289				299				289	299	296
Ending balance: Individually evaluated for impairment		0				0				0	0
Ending balance: Collectively evaluated for impairment		289				299				289	299
Finance Receivables:
Total Finance Receivables		50,363				50,302				50,363	50,302
Ending balance: Individually evaluated for impairment		0				0				0	0
Ending balance: Collectively evaluated for impairment		50,363				50,302				50,363	50,302
Finance Receivables, Net [Member] | Commercial Portfolio Segment [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period					2				2	2	2
Charge-offs										(1)	(2)
Recoveries										0	1
Provisions										1	1
Transferred to held-for-sale										(2)
Allowance for credit losses at end of period		0				2				0	2	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				521				0	521
Ending balance: Individually evaluated for impairment		0				0				0	0
Ending balance: Collectively evaluated for impairment		0				521				0	521
Finance Receivables, Net [Member] | Dealer Products [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at beginning of period					$ 108				$ 88	108	88
Charge-offs										0	(1)
Recoveries										0	1
Provisions										28	20
Transferred to held-for-sale										(4)
Allowance for credit losses at end of period		132				108				132	108	$ 88
Ending balance: Individually evaluated for impairment		54				55				54	55
Ending balance: Collectively evaluated for impairment		78				53				78	53
Finance Receivables:
Total Finance Receivables		15,899				15,744				15,899	15,744
Ending balance: Individually evaluated for impairment		540				360				540	360
Ending balance: Collectively evaluated for impairment		$ 15,359				$ 15,384				$ 15,359	$ 15,384

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