Finance Receivables - Delinquency (Details) - Retail Finance Receivables [Member] - Automobile Loan [Member] - USD ($) $ in Millions	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
In repossession	$ 57	$ 43
In repossession (percent)	0.10%	0.20%
Total finance receivables more than 30 days delinquent or in repossession	$ 1,697	$ 1,583
Total finance receivables more than 30 days delinquent or in repossession (percent)	4.70%	5.10%
31 to 60 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable past due	$ 1,178	$ 1,076
Financing receivable past due (percent)	3.30%	3.40%
Greater Than 60 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable past due	$ 462	$ 464
Financing receivable past due (percent)	1.30%	1.50%
Thirty or More Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable past due	$ 1,640	$ 1,540
Financing receivable past due (percent)	4.60%	4.90%