Fair Value Measurements - Assets and Liabilities Not Carried at Fair Value on Recurring Basis on Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2021	Mar. 31, 2021
Unsecured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	$ 84,689
Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	27,020
Fair value [Member] | Unsecured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	85,859	$ 86,760
Fair value [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	27,270	24,478
Fair value [Member] | Level 1 [Member] | Unsecured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	0	0
Fair value [Member] | Level 1 [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	0	0
Fair value [Member] | Level 2 [Member] | Unsecured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	85,834	86,205
Fair value [Member] | Level 2 [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	0	0
Fair value [Member] | Level 3 [Member] | Unsecured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	25	555
Fair value [Member] | Level 3 [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	27,270	24,478
Carrying value [Member] | Unsecured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities		85,513
Carrying value [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities		24,212
Retail Loan [Member]
Financial assets
Finance receivables, net	69,833
Retail Loan [Member] | Fair value [Member]
Financial assets
Finance receivables, net	73,449	69,007
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	73,449	69,007
Retail Loan [Member] | Carrying value [Member]
Financial assets
Finance receivables, net		65,808
Wholesale [Member]
Financial assets
Finance receivables, net	2,911
Wholesale [Member] | Fair value [Member]
Financial assets
Finance receivables, net	2,927	6,158
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	2,927	6,158
Wholesale [Member] | Carrying value [Member]
Financial assets
Finance receivables, net		6,132
Real estate [Member]
Financial assets
Finance receivables, net	5,040
Real estate [Member] | Fair value [Member]
Financial assets
Finance receivables, net	5,403	5,224
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	5,403	5,224
Real estate [Member] | Carrying value [Member]
Financial assets
Finance receivables, net		5,142
Working capital [Member]
Financial assets
Finance receivables, net	1,885
Working capital [Member] | Fair value [Member]
Financial assets
Finance receivables, net	1,870	2,171
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	$ 1,870	2,171
Working capital [Member] | Carrying value [Member]
Financial assets
Finance receivables, net		$ 2,154