Debt - Schedule of Debt (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Short Term and Long Term Debt [Line Items]
Secured debt	$ 39,441	$ 39,887
Unsecured debt	44,079	40,830
Total secured and unsecured debt	83,520	80,717
Secured debt fair value	39,395	39,948
Unsecured debt fair value	44,738	41,989
Fair value of Secured and Unsecured debt	84,133	81,937
Level 2 [Member]
Short Term and Long Term Debt [Line Items]
Fair value of Secured and Unsecured debt	81,931	79,623
Level 3 [Member]
Short Term and Long Term Debt [Line Items]
Fair value of Secured and Unsecured debt	2,202	2,314
Revolving Credit Facility [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	3,587	4,694
Unsecured debt	2,311	2,368
Secured debt fair value	3,605	4,713
Unsecured debt fair value	2,314	2,375
Securitization Notes Payable [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	35,854	35,193
Securitization Notes Payable [Member] | Retail Finance Receivables [Member]
Short Term and Long Term Debt [Line Items]
Secured debt fair value	35,790	35,235
Senior Notes [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	40,056	36,820
Unsecured debt fair value	40,708	37,969
Other Unsecured Debt [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	1,712	1,642
Unsecured debt fair value	$ 1,716	$ 1,645