Finance Receivables - Finance Receivables, net (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables, net	$ 48,080	$ 42,172
Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value utilizing inputs	11,044	10,259
Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value utilizing inputs	36,676	31,919
Commercial Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total finance receivables	11,105	10,312
Automobile Loan [Member] | Retail Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment, net of fees	35,567	30,574
Individually evaluated for impairment, net of fees	2,308	2,228
Total finance receivables	37,875	32,802
Less: allowance for loan losses - collective	(522)	(561)
Less: allowance for loan losses - specific	(317)	(328)
Total finance receivables, net	37,036	31,913
Deferred income	104	228
Automobile Loan [Member] | Commercial Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment, net of fees	11,038	10,290
Individually evaluated for impairment, net of fees	67	22
Total finance receivables	11,105	10,312
Less: allowance for loan losses - collective	(53)	(50)
Less: allowance for loan losses - specific	(8)	(3)
Total finance receivables, net	$ 11,044	$ 10,259