Fair Value Measurements - Assets and Liabilities Not Carried at Fair Value on Recurring Basis on Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021
Unsecured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	$ 84,233
Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	24,900
Fair value [Member] | Unsecured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	85,617	$ 86,760
Fair value [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	25,169	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	85,562	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	55	555
Fair value [Member] | Level 3 [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	25,169	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	67,974
Retail Loan [Member] | Fair value [Member]
Financial assets
Finance receivables, net	71,323	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	71,323	69,007
Retail Loan [Member] | Carrying value [Member]
Financial assets
Finance receivables, net		65,808
Wholesale [Member]
Financial assets
Finance receivables, net	3,570
Wholesale [Member] | Fair value [Member]
Financial assets
Finance receivables, net	3,591	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	3,591	6,158
Wholesale [Member] | Carrying value [Member]
Financial assets
Finance receivables, net		6,132
Real estate [Member]
Financial assets
Finance receivables, net	5,038
Real estate [Member] | Fair value [Member]
Financial assets
Finance receivables, net	5,149	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	5,149	5,224
Real estate [Member] | Carrying value [Member]
Financial assets
Finance receivables, net		5,142
Working capital [Member]
Financial assets
Finance receivables, net	1,992
Working capital [Member] | Fair value [Member]
Financial assets
Finance receivables, net	1,959	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	$ 1,959	2,171
Working capital [Member] | Carrying value [Member]
Financial assets
Finance receivables, net		$ 2,154