Fair Value Measurements - Assets and Liabilities Not Carried at Fair Value on Recurring Basis on Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Mar. 31, 2020
Carrying value [Member] | Unsecured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	$ 85,422	$ 83,172
Carrying value [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	20,480	14,568
Fair value [Member] | Unsecured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	87,534	82,989
Fair value [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	20,831	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	87,043	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	491	560
Fair value [Member] | Level 3 [Member] | Secured Notes and Loans Payable [Member]
Financial liabilities
Financial liabilities	20,831	14,608
Retail Loan [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	61,249	56,360
Retail Loan [Member] | Fair value [Member]
Financial assets
Finance receivables, net	64,583	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	64,583	57,303
Wholesale [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	5,999	9,672
Wholesale [Member] | Fair value [Member]
Financial assets
Finance receivables, net	6,045	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	6,045	9,637
Real estate [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	4,876	4,544
Real estate [Member] | Fair value [Member]
Financial assets
Finance receivables, net	4,858	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	4,858	4,140
Working capital [Member] | Carrying value [Member]
Financial assets
Finance receivables, net	2,244	3,308
Working capital [Member] | Fair value [Member]
Financial assets
Finance receivables, net	2,111	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	$ 2,111	$ 2,811