Finance Receivables, Net (Summary of Impaired Loans by Class of Finance Receivable) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Mar. 31, 2016
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	$ 193		$ 193		$ 254
Impaired Finance Receivables Individually Evaluated with No Related Allowance	242		242		286
Impaired Finance Receivables Aggregated And Evaluated For Impairment	224		224		226
Impaired Finance Receivables	659		659		766
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	193		193		254
Unpaid Principal Balance Individually Evaluated with No Related Allowance	242		242		286
Unpaid Principal Balance Aggregated And Evaluated For Impairment	221		221		223
Unpaid Principal Balance	656		656		763
Individually Evaluated Allowance	27		27		54
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	179	$ 211	204	$ 195
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	272	193	277	195
Average Impaired Finance Receivables Account Balances Aggregated And Evaluated For Impairment	224	252	225	256
Average Impaired Finance Receivables	675	656	706	646
Interest Income Recognized
Interest Income Recognized Individually Evaluated with Related Allowance	2	2	3	3
Interest Income Recognized Individually Evaluated with No Related Allowance	2	2	5	3
Interest Income Recognized Aggregated And Evaluated For Impairment	4	4	8	9
Interest Income Recognized	8	8	16	15
Wholesale [Member]
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	77		77		98
Impaired Finance Receivables Individually Evaluated with No Related Allowance	125		125		185
Impaired Finance Receivables	202		202		283
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	77		77		98
Unpaid Principal Balance Individually Evaluated with No Related Allowance	125		125		185
Unpaid Principal Balance	202		202		283
Individually Evaluated Allowance	6		6		9
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	59	88	72	84
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	160	104	168	105
Average Impaired Finance Receivables	219	192	240	189
Interest Income Recognized
Interest Income Recognized Individually Evaluated with Related Allowance	1	1	1	1
Interest Income Recognized Individually Evaluated with No Related Allowance	0	1	2	1
Interest Income Recognized	1	2	3	2
Real estate [Member]
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	83		83		119
Impaired Finance Receivables Individually Evaluated with No Related Allowance	117		117		98
Impaired Finance Receivables	200		200		217
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	83		83		119
Unpaid Principal Balance Individually Evaluated with No Related Allowance	117		117		98
Unpaid Principal Balance	200		200		217
Individually Evaluated Allowance	12		12		15
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	87	88	98	76
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	112	85	108	87
Average Impaired Finance Receivables	199	173	206	163
Interest Income Recognized
Interest Income Recognized Individually Evaluated with Related Allowance	0	0	1	1
Interest Income Recognized Individually Evaluated with No Related Allowance	2	1	3	2
Interest Income Recognized	2	1	4	3
Working capital [Member]
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	33		33		37
Impaired Finance Receivables Individually Evaluated with No Related Allowance	0		0		3
Impaired Finance Receivables	33		33		40
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	33		33		37
Unpaid Principal Balance Individually Evaluated with No Related Allowance	0		0		3
Unpaid Principal Balance	33		33		40
Individually Evaluated Allowance	9		9		30
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	33	35	34	35
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	0	4	1	3
Average Impaired Finance Receivables	33	39	35	38
Interest Income Recognized
Interest Income Recognized Individually Evaluated with Related Allowance	1	1	1	1
Interest Income Recognized Individually Evaluated with No Related Allowance	0	0	0	0
Interest Income Recognized	1	1	1	1
Retail Loan [Member]
Impaired Finance Receivables
Impaired Finance Receivables Aggregated And Evaluated For Impairment	224		224		226
Impaired Finance Receivables	224		224		226
Unpaid Principal Balance
Unpaid Principal Balance Aggregated And Evaluated For Impairment	221		221		223
Unpaid Principal Balance	221		221		$ 223
Average Impaired Finance Receivables
Average Impaired Finance Receivables Account Balances Aggregated And Evaluated For Impairment	224	252	225	256
Average Impaired Finance Receivables	224	252	225	256
Interest Income Recognized
Interest Income Recognized Aggregated And Evaluated For Impairment	4	4	8	9
Interest Income Recognized	$ 4	$ 4	$ 8	$ 9