Debt - Short Term and Long Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Short Term and Long Term Debt [Line Items]
Secured debt	$ 35,237	$ 30,689
Unsecured debt	33,526	23,657
Long-term Debt	68,763	54,346
Secured debt fair value	35,418	30,671
Unsecured debt fair value	34,389	23,726
Fair value of Secured and Unsecured debt	69,807	54,397
Level 2 [Member]
Short Term and Long Term Debt [Line Items]
Fair value of Secured and Unsecured debt	64,847	48,716
Level 3 [Member]
Short Term and Long Term Debt [Line Items]
Fair value of Secured and Unsecured debt	4,960	5,681
Revolving Credit Facility [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	7,947	7,548
Unsecured debt	3,676	2,759
Secured debt fair value	7,944	7,494
Unsecured debt fair value	3,678	2,753
Securitization Notes Payable [Member] | Retail Finance Receivables [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	27,290	23,141
Secured debt fair value	27,474	23,177
Senior Notes [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	27,199	18,973
Unsecured debt fair value	28,053	19,045
Retail Customer Deposits [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	1,929	1,260
Unsecured debt fair value	1,936	1,262
Other Unsecured Debt [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	722	665
Unsecured debt fair value	$ 722	$ 666