Fair Value Measurements - Assets and Liabilities Not Carried at Fair Value on Recurring Basis on Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Carrying value [Member]
Financial liabilities
Unsecured notes and loans payable	$ 80,521	$ 84,715
Secured notes and loans payable	12,401	13,638
Fair value [Member]
Financial liabilities
Unsecured notes and loans payable	81,369	85,095
Secured notes and loans payable	12,428	13,588
Fair value [Member] | Level 1 [Member]
Financial liabilities
Unsecured notes and loans payable	0	0
Secured notes and loans payable	0	0
Fair value [Member] | Level 2 [Member]
Financial liabilities
Unsecured notes and loans payable	79,056	82,754
Secured notes and loans payable	0	0
Fair value [Member] | Level 3 [Member]
Financial liabilities
Unsecured notes and loans payable	2,313	2,341
Secured notes and loans payable	12,428	13,588
Retail Loan [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	53,013	52,374
Retail Loan [Member] | Fair value [Member]
Financial assets
Finance receivables, net	53,247	52,081
Retail Loan [Member] | Fair value [Member] | Level 1 [Member]
Financial assets
Finance receivables, net	0	0
Retail Loan [Member] | Fair value [Member] | Level 2 [Member]
Financial assets
Finance receivables, net	0	0
Retail Loan [Member] | Fair value [Member] | Level 3 [Member]
Financial assets
Finance receivables, net	53,247	52,081
Wholesale [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	10,293	10,365
Wholesale [Member] | Fair value [Member]
Financial assets
Finance receivables, net	10,369	10,413
Wholesale [Member] | Fair value [Member] | Level 1 [Member]
Financial assets
Finance receivables, net	0	0
Wholesale [Member] | Fair value [Member] | Level 2 [Member]
Financial assets
Finance receivables, net	0	0
Wholesale [Member] | Fair value [Member] | Level 3 [Member]
Financial assets
Finance receivables, net	10,369	10,413
Real estate [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	4,550	4,492
Real estate [Member] | Fair value [Member]
Financial assets
Finance receivables, net	4,534	4,409
Real estate [Member] | Fair value [Member] | Level 1 [Member]
Financial assets
Finance receivables, net	0	0
Real estate [Member] | Fair value [Member] | Level 2 [Member]
Financial assets
Finance receivables, net	0	0
Real estate [Member] | Fair value [Member] | Level 3 [Member]
Financial assets
Finance receivables, net	4,534	4,409
Working capital [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	2,510	2,222
Working capital [Member] | Fair value [Member]
Financial assets
Finance receivables, net	2,554	2,197
Working capital [Member] | Fair value [Member] | Level 1 [Member]
Financial assets
Finance receivables, net	0	0
Working capital [Member] | Fair value [Member] | Level 2 [Member]
Financial assets
Finance receivables, net	0	0
Working capital [Member] | Fair value [Member] | Level 3 [Member]
Financial assets
Finance receivables, net	$ 2,554	$ 2,197