Fair Value Measurements - Assets and Liabilities Not Carried at Fair Value on Recurring Basis on Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019
Carrying value [Member]
Financial liabilities
Unsecured notes and loans payable	$ 84,468	$ 80,521
Secured notes and loans payable	12,916	12,401
Fair value [Member]
Financial liabilities
Unsecured notes and loans payable	85,765	81,369
Secured notes and loans payable	13,013	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	84,190	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	13,013	12,428
Retail Loan [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	54,170	53,013
Retail Loan [Member] | Fair value [Member]
Financial assets
Finance receivables, net	54,867	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	54,867	53,247
Wholesale [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	10,653	10,293
Wholesale [Member] | Fair value [Member]
Financial assets
Finance receivables, net	10,724	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	10,724	10,369
Real estate [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	4,604	4,550
Real estate [Member] | Fair value [Member]
Financial assets
Finance receivables, net	4,653	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	4,653	4,534
Working capital [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	2,539	2,510
Working capital [Member] | Fair value [Member]
Financial assets
Finance receivables, net	2,587	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	$ 2,587	$ 2,554