Fair Value Measurements - Assets and Liabilities Not Carried at Fair Value on Recurring Basis on Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2018	Mar. 31, 2018
Carrying value [Member]
Financial liabilities
Commercial paper	$ 25,287	$ 27,313
Unsecured notes and loans payable	58,412	57,402
Secured notes and loans payable	14,529	13,638
Fair value [Member]
Financial liabilities
Commercial paper	25,287	27,313
Unsecured notes and loans payable	58,526	57,782
Secured notes and loans payable	14,499	13,588
Fair value [Member] \| Level 1 [Member]
Financial liabilities
Commercial paper	0	0
Unsecured notes and loans payable	0	0
Secured notes and loans payable	0	0
Fair value [Member] \| Level 2 [Member]
Financial liabilities
Commercial paper	25,287	27,313
Unsecured notes and loans payable	56,229	55,441
Secured notes and loans payable	0	0
Fair value [Member] \| Level 3 [Member]
Financial liabilities
Commercial paper	0	0
Unsecured notes and loans payable	2,297	2,341
Secured notes and loans payable	14,499	13,588
Retail Loan [Member] \| Carrying value [Member]
Financial assets
Finance receivables, net	52,926	52,374
Retail Loan [Member] \| Fair value [Member]
Financial assets
Finance receivables, net	52,444	52,081
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	52,444	52,081
Wholesale [Member] \| Carrying value [Member]
Financial assets
Finance receivables, net	9,514	10,365
Wholesale [Member] \| Fair value [Member]
Financial assets
Finance receivables, net	9,557	10,413
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	9,557	10,413
Real estate [Member] \| Carrying value [Member]
Financial assets
Finance receivables, net	4,421	4,492
Real estate [Member] \| Fair value [Member]
Financial assets
Finance receivables, net	4,366	4,409
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	4,366	4,409
Working capital [Member] \| Carrying value [Member]
Financial assets
Finance receivables, net	2,288	2,222
Working capital [Member] \| Fair value [Member]
Financial assets
Finance receivables, net	2,314	2,197
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	$ 2,314	$ 2,197

Fair value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

No definition available.

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- Definition

Fair value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

No definition available.

+ Details

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- Definition

Including the current and noncurrent portions, fair value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

+ References

No definition available.

+ Details

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- References

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- References

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

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