Finance Receivables - Credit Risk Profile by Dealer grouping of Commercial Finance Receivables (Details) - Commercial Finance Receivables [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 9,495	$ 7,880
Percent of portfolio	100.00%	100.00%
Group I [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 1,547	$ 1,389
Percent of portfolio	16.30%	17.60%
Group II [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 3,565	$ 2,661
Percent of portfolio	37.50%	33.80%
Group III [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 3,112	$ 2,775
Percent of portfolio	32.80%	35.20%
Group IV [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 931	$ 631
Percent of portfolio	9.80%	8.00%
Group V [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 238	$ 334
Percent of portfolio	2.50%	4.20%
Group VI [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at end of period	$ 102	$ 90
Percent of portfolio	1.10%	1.20%