Fair Value Measurements - Assets and Liabilities Not Carried at Fair Value on Recurring Basis on Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Mar. 31, 2019
Carrying value [Member]
Financial liabilities
Unsecured notes and loans payable	$ 82,256	$ 80,521
Secured notes and loans payable	12,837	12,401
Fair value [Member]
Financial liabilities
Unsecured notes and loans payable	83,685	81,369
Secured notes and loans payable	12,954	12,428
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	82,110	79,056
Secured notes and loans payable	0	0
Fair value [Member] | Level 3 [Member]
Financial liabilities
Unsecured notes and loans payable	1,575	2,313
Secured notes and loans payable	12,954	12,428
Retail Loan [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	55,842	53,013
Retail Loan [Member] | Fair value [Member]
Financial assets
Finance receivables, net	56,665	53,247
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	56,665	53,247
Wholesale [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	9,892	10,293
Wholesale [Member] | Fair value [Member]
Financial assets
Finance receivables, net	9,977	10,369
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	9,977	10,369
Real estate [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	4,575	4,550
Real estate [Member] | Fair value [Member]
Financial assets
Finance receivables, net	4,676	4,534
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	4,676	4,534
Working capital [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	2,567	2,510
Working capital [Member] | Fair value [Member]
Financial assets
Finance receivables, net	2,593	2,554
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	$ 2,593	$ 2,554