Finance Receivables, Net (Summary of Impaired Loans by Class of Finance Receivable) (Details) - USD ($) $ in Millions	3 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	$ 217		$ 248
Impaired Finance Receivables Individually Evaluated with No Related Allowance	265		247
Impaired Finance Receivables	707		717
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	217		248
Unpaid Principal Balance Individually Evaluated with No Related Allowance	265		247
Unpaid Principal Balance	705		715
Individually Evaluated Allowance	62		70
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	232	$ 242
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	256	234
Average Impaired Finance Receivables	712	698
Wholesale [Member]
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	111		107
Impaired Finance Receivables Individually Evaluated with No Related Allowance	103		83
Impaired Finance Receivables	214		190
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	111		107
Unpaid Principal Balance Individually Evaluated with No Related Allowance	103		83
Unpaid Principal Balance	214		190
Individually Evaluated Allowance	10		14
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	109	109
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	93	134
Average Impaired Finance Receivables	202	243
Real estate [Member]
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	54		86
Impaired Finance Receivables Individually Evaluated with No Related Allowance	141		142
Impaired Finance Receivables	195		228
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	54		86
Unpaid Principal Balance Individually Evaluated with No Related Allowance	141		142
Unpaid Principal Balance	195		228
Individually Evaluated Allowance	3		5
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	70	94
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	141	100
Average Impaired Finance Receivables	211	194
Working capital [Member]
Impaired Finance Receivables
Impaired Finance Receivables Individually Evaluated with Related Allowance	52		55
Impaired Finance Receivables Individually Evaluated with No Related Allowance	21		22
Impaired Finance Receivables	73		77
Unpaid Principal Balance
Unpaid Principal Balance Individually Evaluated with Related Allowance	52		55
Unpaid Principal Balance Individually Evaluated with No Related Allowance	21		22
Unpaid Principal Balance	73		77
Individually Evaluated Allowance	49		51
Average Impaired Finance Receivables
Average Impaired Finance Receivables Individually Evaluated For Impairment with An Allowance	53	39
Average Impaired Finance Receivables Individually Evaluated For Impairment Without An Allowance	22	0
Average Impaired Finance Receivables	75	39
Retail Loan [Member]
Impaired Finance Receivables
Impaired Finance Receivables Aggregated And Evaluated For Impairment	225		222
Impaired Finance Receivables	225		222
Unpaid Principal Balance
Unpaid Principal Balance Aggregated And Evaluated For Impairment	223		220
Unpaid Principal Balance	223		$ 220
Average Impaired Finance Receivables
Average Impaired Finance Receivables Account Balances Aggregated And Evaluated For Impairment	224	222
Average Impaired Finance Receivables	$ 224	$ 222

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