Finance Receivables - Credit Risk Profile by Dealer grouping of Commercial Finance Receivables (Details) - Commercial Finance Receivables [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 12,721	$ 10,312
Concentration risk (percent)	100.00%	100.00%
Group I [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 2,192	$ 1,915
Concentration risk (percent)	17.20%	18.60%
Group II [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 4,500	$ 3,584
Concentration risk (percent)	35.40%	34.70%
Group III [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 4,292	$ 3,424
Concentration risk (percent)	33.70%	33.20%
Group IV [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 1,205	$ 1,048
Concentration risk (percent)	9.50%	10.20%
Group V [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 449	$ 260
Concentration risk (percent)	3.50%	2.50%
Group VI [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 83	$ 81
Concentration risk (percent)	0.70%	0.80%