Finance Receivables, Net (Impaired Finance Receivables) (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
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	$ 71		$ 71		$ 73
Impaired Finance Receivables Individually Evaluated with No Related Allowance	149		149		168
Impaired Finance Receivables Aggregated And Evaluated For Impairment	367		367		416
Impaired Finance Receivables	587		587		657
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	71		71		73
Unpaid Principal Balance Individually Evaluated with No Related Allowance	149		149		168
Unpaid Principal Balance Aggregated And Evaluated For Impairment	363		363		411
Unpaid Principal Balance	583		583		652
Individually Evaluated Allowance	33		33		33
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	78	146	76	148
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	151	112	157	95
Average Impaired Finance Receivables Account Balances Aggregated And Evaluated For Impairment	379	474	391	484
Average Impaired Finance Receivables	608	732	624	727
Interest Income Recognized
Interest Income Recognized Individually Evaluated with Related Allowance	1	1	2	2
Interest Income Recognized Individually Evaluated with No Related Allowance	1	3	2	3
Interest Income Recognized Aggregated And Evaluated For Impairment	7	9	15	19
Interest Income Recognized	9	13	19	24
Wholesale [Member]
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	13		13		16
Impaired Finance Receivables Individually Evaluated with No Related Allowance	52		52		66
Impaired Finance Receivables	65		65		82
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	13		13		16
Unpaid Principal Balance Individually Evaluated with No Related Allowance	52		52		66
Unpaid Principal Balance	65		65		82
Individually Evaluated Allowance	1		1		3
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	18	30	17	22
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	53	61	58	61
Average Impaired Finance Receivables	71	91	75	83
Interest Income Recognized
Interest Income Recognized Individually Evaluated with Related Allowance	0	0	0	0
Interest Income Recognized Individually Evaluated with No Related Allowance	0	1	0	1
Interest Income Recognized	0	1	0	1
Real estate [Member]
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	34		34		33
Impaired Finance Receivables Individually Evaluated with No Related Allowance	92		92		97
Impaired Finance Receivables	126		126		130
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	34		34		33
Unpaid Principal Balance Individually Evaluated with No Related Allowance	92		92		97
Unpaid Principal Balance	126		126		130
Individually Evaluated Allowance	9		9		7
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	36	86	35	103
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	93	50	94	33
Average Impaired Finance Receivables	129	136	129	136
Interest Income Recognized
Interest Income Recognized Individually Evaluated with Related Allowance	1	0	1	1
Interest Income Recognized Individually Evaluated with No Related Allowance	1	2	2	2
Interest Income Recognized	2	2	3	3
Working capital [Member]
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	24		24		24
Impaired Finance Receivables Individually Evaluated with No Related Allowance	5		5		5
Impaired Finance Receivables	29		29		29
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	24		24		24
Unpaid Principal Balance Individually Evaluated with No Related Allowance	5		5		5
Unpaid Principal Balance	29		29		29
Individually Evaluated Allowance	23		23		23
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	24	30	24	23
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	5	1	5	1
Average Impaired Finance Receivables	29	31	29	24
Interest Income Recognized
Interest Income Recognized Individually Evaluated with Related Allowance	0	1	1	1
Interest Income Recognized Individually Evaluated with No Related Allowance	0	0	0	0
Interest Income Recognized	0	1	1	1
Retail Loan [Member]
Impaired Finance Receivables
Impaired Finance Receivables Aggregated And Evaluated For Impairment	366		366		415
Impaired Finance Receivables	366		366		415
Unpaid Principal Balance
Unpaid Principal Balance Aggregated And Evaluated For Impairment	362		362		410
Unpaid Principal Balance	362		362		410
Average Impaired Finance Receivables
Average Impaired Finance Receivables Account Balances Aggregated And Evaluated For Impairment	378	473	390	483
Average Impaired Finance Receivables	378	473	390	483
Interest Income Recognized
Interest Income Recognized Aggregated And Evaluated For Impairment	7	9	15	19
Interest Income Recognized	7	9	15	19
Commercial [Member]
Impaired Finance Receivables
Impaired Finance Receivables Aggregated And Evaluated For Impairment	1		1		1
Impaired Finance Receivables	1		1		1
Unpaid Principal Balance
Unpaid Principal Balance Aggregated And Evaluated For Impairment	1		1		1
Unpaid Principal Balance	1		1		1
Average Impaired Finance Receivables
Average Impaired Finance Receivables Account Balances Aggregated And Evaluated For Impairment	1	1	1	1
Average Impaired Finance Receivables	1	1	1	1
Interest Income Recognized
Interest Income Recognized Aggregated And Evaluated For Impairment	0	0	0	0
Interest Income Recognized	$ 0	$ 0	$ 0	$ 0