Debt - Short Term and Long Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Short Term and Long Term Debt [Line Items]
Secured debt	$ 39,270	$ 30,689
Secured Debt, Fair Value Disclosure	39,357	30,671
Unsecured debt	34,606	23,657
Unsecured Debt, Fair Value Disclosure	35,220	23,726
Long-term Debt	73,876	54,346
Long-term Debt, Fair Value	74,577	54,397
Fair Value, Inputs, Level 2 [Member]
Short Term and Long Term Debt [Line Items]
Long-term Debt, Fair Value	69,990	48,716
Fair Value, Inputs, Level 3 [Member]
Short Term and Long Term Debt [Line Items]
Long-term Debt, Fair Value	4,587	5,681
Revolving Credit Facility [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	9,817	7,548
Secured Debt, Fair Value Disclosure	9,812	7,494
Unsecured debt	3,354	2,759
Unsecured Debt, Fair Value Disclosure	3,354	2,753
Senior Notes [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	28,577	18,973
Unsecured Debt, Fair Value Disclosure	29,182	19,045
Retail Customer Deposits [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	1,895	1,260
Unsecured Debt, Fair Value Disclosure	1,902	1,262
Other Unsecured Debt [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	780	665
Unsecured Debt, Fair Value Disclosure	782	666
Retail Finance Receivables [Member] | Securitization Notes Payable [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	29,453	23,141
Secured Debt, Fair Value Disclosure	$ 29,545	$ 23,177