Debt - Short Term and Long Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Short Term and Long Term Debt [Line Items]
Secured debt	$ 39,959	$ 42,835
Secured Debt, Fair Value Disclosure	40,160	42,835
Unsecured debt	48,979	48,153
Unsecured Debt, Fair Value Disclosure	50,239	47,556
Total Debt	88,938	90,988
Long-term Debt, Fair Value	90,399	90,391
Fair Value, Inputs, Level 2 [Member]
Short Term and Long Term Debt [Line Items]
Long-term Debt, Fair Value	88,481	88,305
Fair Value, Inputs, Level 3 [Member]
Short Term and Long Term Debt [Line Items]
Long-term Debt, Fair Value	1,918	2,086
Revolving Credit Facility [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	6,152	3,410
Secured Debt, Fair Value Disclosure	6,160	3,413
Unsecured debt	1,936	2,157
Unsecured Debt, Fair Value Disclosure	1,936	2,151
Securitization Notes Payable [Member]
Short Term and Long Term Debt [Line Items]
Secured debt	33,807	39,425
Secured Debt, Fair Value Disclosure	34,000	39,422
Senior Notes [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	43,679	42,611
Unsecured Debt, Fair Value Disclosure	44,937	42,015
Other Unsecured Debt [Member]
Short Term and Long Term Debt [Line Items]
Unsecured debt	3,364	3,385
Unsecured Debt, Fair Value Disclosure	$ 3,366	$ 3,390