Debt - Schedule of Debt (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Short Term and Long Term Debt [Line Items]
Secured debt	$ 40,775	$ 35,087
Unsecured debt	38,263	29,476
Total secured and unsecured debt	79,038	64,563
Secured debt fair value	40,889	35,162
Unsecured debt fair value	39,411	30,045
Fair value of Secured and Unsecured debt	80,300	65,207
Level 2 [Member]
Short Term and Long Term Debt [Line Items]
Fair value of Secured and Unsecured debt	78,293	62,951
Level 3 [Member]
Short Term and Long Term Debt [Line Items]
Fair value of Secured and Unsecured debt	2,007	2,256
Revolving Credit Facility [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	4,751	8,503
Unsecured debt	2,162	1,961
Secured debt fair value	4,769	8,498
Unsecured debt fair value	2,174	1,961
Securitization Notes Payable [Member] | Retail Finance Receivables [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	36,024	26,584
Secured debt fair value	36,120	26,664
Senior Notes [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	34,794	26,737
Unsecured debt fair value	35,927	27,304
Other Unsecured Debt [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	1,307	778
Unsecured debt fair value	$ 1,310	$ 780