Fair Value Measurements - Assets and Liabilities Not Carried at Fair Value on Recurring Basis on Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020
Carrying value [Member] | Unsecured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	$ 85,513	$ 83,172
Carrying value [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	24,212	14,568
Fair value [Member] | Unsecured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	86,760	82,989
Fair value [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	24,478	14,608
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	86,205	82,429
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	555	560
Fair value [Member] | Level 3 [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	24,478	14,608
Retail Loan [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	65,808	56,360
Retail Loan [Member] | Fair value [Member]
Financial assets
Finance receivables, net	69,007	57,303
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	69,007	57,303
Wholesale [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	6,132	9,672
Wholesale [Member] | Fair value [Member]
Financial assets
Finance receivables, net	6,158	9,637
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	6,158	9,637
Real estate [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	5,142	4,544
Real estate [Member] | Fair value [Member]
Financial assets
Finance receivables, net	5,224	4,140
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	5,224	4,140
Working capital [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	2,154	3,308
Working capital [Member] | Fair value [Member]
Financial assets
Finance receivables, net	2,171	2,811
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	$ 2,171	$ 2,811