Finance Receivables, Net (Summary of Impaired Loans by Class of Finance Receivable) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	$ 184		$ 184		$ 248
Impaired Finance Receivables Individually Evaluated with No Related Allowance	262		262		247
Impaired Finance Receivables	662		662		717
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	184		184		248
Unpaid Principal Balance Individually Evaluated with No Related Allowance	262		262		247
Unpaid Principal Balance	660		660		715
Individually Evaluated Allowance	57		57		70
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	200	$ 236	216	$ 230
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	264	213	258	222
Average Impaired Finance Receivables	684	671	695	673
Wholesale [Member]
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	95		95		107
Impaired Finance Receivables Individually Evaluated with No Related Allowance	101		101		83
Impaired Finance Receivables	196		196		190
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	95		95		107
Unpaid Principal Balance Individually Evaluated with No Related Allowance	101		101		83
Unpaid Principal Balance	196		196		190
Individually Evaluated Allowance	7		7		14
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	103	101	104	98
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	102	116	96	122
Average Impaired Finance Receivables	205	217	200	220
Real estate [Member]
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	39		39		86
Impaired Finance Receivables Individually Evaluated with No Related Allowance	140		140		142
Impaired Finance Receivables	179		179		228
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	39		39		86
Unpaid Principal Balance Individually Evaluated with No Related Allowance	140		140		142
Unpaid Principal Balance	179		179		228
Individually Evaluated Allowance	2		2		5
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	46	91	60	92
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	141	97	141	100
Average Impaired Finance Receivables	187	188	201	192
Working capital [Member]
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	50		50		55
Impaired Finance Receivables Individually Evaluated with No Related Allowance	21		21		22
Impaired Finance Receivables	71		71		77
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	50		50		55
Unpaid Principal Balance Individually Evaluated with No Related Allowance	21		21		22
Unpaid Principal Balance	71		71		77
Individually Evaluated Allowance	48		48		51
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	51	44	52	40
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	21	0	21	0
Average Impaired Finance Receivables	72	44	73	40
Retail Loan [Member]
Impaired Finance Receivables
Impaired Finance Receivables Aggregated And Evaluated For Impairment	216		216		222
Impaired Finance Receivables	216		216		222
Unpaid Principal Balance
Unpaid Principal Balance Aggregated And Evaluated For Impairment	214		214		220
Unpaid Principal Balance	214		214		$ 220
Average Impaired Finance Receivables
Average Impaired Finance Receivables Account Balances Aggregated And Evaluated For Impairment	220	222	221	221
Average Impaired Finance Receivables	$ 220	$ 222	$ 221	$ 221

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