Finance Receivables - Credit Risk Profile by Dealer grouping of Commercial Finance Receivables (Details) - Commercial Finance Receivables [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 12,368	$ 12,721
Percent of portfolio	100.00%	100.00%
Group I [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 2,075	$ 2,192
Percent of portfolio	16.80%	17.20%
Group II [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 4,897	$ 4,500
Percent of portfolio	39.60%	35.40%
Group III [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 3,737	$ 4,292
Percent of portfolio	30.20%	33.70%
Group IV [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 1,167	$ 1,205
Percent of portfolio	9.40%	9.50%
Group V [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 423	$ 449
Percent of portfolio	3.40%	3.50%
Group VI [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 69	$ 83
Percent of portfolio	0.60%	0.70%