Allowance for Credit Losses and Recorded Investment in Finance Receivables by Portfolio Segment (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at	$ 501	$ 606	$ 527	$ 619
Provision for credit losses	28	3	39	19
Allowance for credit losses at	467	549	467	549
Gross Finance Receivables:
Ending Balance at	64,843		64,843		63,172
Retail Loan [Member]
Gross Finance Receivables:
Gross Finance Receivables	366	471	366	471
Commercial [Member]
Gross Finance Receivables:
Gross Finance Receivables	1	1	1	1
Finance Receivables, Net [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at	424	515	445	524
Charge-offs	(67)	(65)	(117)	(110)
Recoveries	16	15	35	33
Provision for credit losses	23	(5)	33	13
Allowance for credit losses at	396	460	396	460
Ending Balance: Individually Evaluated for Impairment	33	45	33	45
Ending Balance: Collectively Evaluated for Impairment	363	415	363	415
Gross Finance Receivables:
Ending Balance at	64,843	61,672	64,843	61,672	63,172
Ending Balance: Individually Evaluated for Impairment	220	258	220	258
Ending Balance: Collectively Evaluated for Impairment	64,623	61,414	64,623	61,414
Finance Receivables, Net [Member] | Retail Loan [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at	309	356		395
Charge-offs	(67)	(65)	(116)	(109)
Recoveries	16	15	35	33
Provision for credit losses	32	27	38	14
Allowance for credit losses at	290	333	290	333
Ending Balance: Individually Evaluated for Impairment	0	0	0	0
Ending Balance: Collectively Evaluated for Impairment	290	333	290	333
Gross Finance Receivables:
Ending Balance at	49,591	47,355	49,591	47,355
Ending Balance: Individually Evaluated for Impairment	0	0	0	0
Ending Balance: Collectively Evaluated for Impairment	49,591	47,355	49,591	47,355
Finance Receivables, Net [Member] | Commercial [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at	3	6	5	10
Charge-offs	0	0	(1)	(1)
Recoveries	0	0	0	0
Provision for credit losses	1	(1)	0	(4)
Allowance for credit losses at	4	5	4	5
Ending Balance: Individually Evaluated for Impairment	0	0	0	0
Ending Balance: Collectively Evaluated for Impairment	4	5	4	5
Gross Finance Receivables:
Ending Balance at	395	361	395	361
Ending Balance: Individually Evaluated for Impairment	0	0	0	0
Ending Balance: Collectively Evaluated for Impairment	395	361	395	361
Finance Receivables, Net [Member] | Dealer Products [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at	112	153	107	119
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	(10)	(31)	(5)	3
Allowance for credit losses at	102	122	102	122
Ending Balance: Individually Evaluated for Impairment	33	45	33	45
Ending Balance: Collectively Evaluated for Impairment	69	77	69	77
Gross Finance Receivables:
Ending Balance at	14,857	13,956	14,857	13,956
Ending Balance: Individually Evaluated for Impairment	220	258	220	258
Ending Balance: Collectively Evaluated for Impairment	14,637	13,698	14,637	13,698
Investments In Operating Leases, Net [Member]
Allowance for Credit Losses for Finance Receivables:
Allowance for credit losses at					82
Allowance for credit losses at	$ 71		$ 71		$ 82