Debt - Short Term and Long Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Short Term and Long Term Debt [Line Items]
Secured debt	$ 30,689	$ 25,173
Unsecured debt	23,657	12,142
Revolving Credit Facility [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	7,548	7,028
Unsecured debt	2,759	2,974
Securitization Notes Payable [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	23,141	18,145
Senior Notes [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	18,973	8,375
Retail Customer Deposits [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	1,260	0
Other Unsecured Debt [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	665	793
North America [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	23,151	15,422
Unsecured debt	17,731	7,777
North America [Member] | Revolving Credit Facility [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	3,246	1,701
Unsecured debt	0	0
North America [Member] | Securitization Notes Payable [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	19,905	13,721
North America [Member] | Senior Notes [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	17,731	7,777
North America [Member] | Retail Customer Deposits [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	0	0
North America [Member] | Other Unsecured Debt [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	0	0
International [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	7,538	9,751
Unsecured debt	5,926	4,365
International [Member] | Revolving Credit Facility [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	4,302	5,327
Unsecured debt	2,759	2,974
International [Member] | Securitization Notes Payable [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	3,236	4,424
International [Member] | Senior Notes [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	1,242	598
International [Member] | Retail Customer Deposits [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	1,260	0
International [Member] | Other Unsecured Debt [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	$ 665	$ 793