Finance Receivables - Credit Risk Profile by Dealer (Details) - Commercial Finance Receivables [Member] - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 13,046	$ 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	$ 1,939	$ 2,192
Percent of portfolio	14.90%	17.20%
Group II [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 5,241	$ 4,500
Percent of portfolio	40.20%	35.40%
Group III [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 4,108	$ 4,292
Percent of portfolio	31.50%	33.70%
Group IV [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 1,229	$ 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	$ 419	$ 449
Percent of portfolio	3.20%	3.50%
Group VI [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 110	$ 83
Percent of portfolio	0.80%	0.70%