Debt (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Average Contractual (interest rate)	2.70%	2.80%
Average Effective (interest rate)	2.90%	3.00%
Unamortized discount	$ (77,000,000)	$ (87,000,000)
Fair value adjustments	190,000,000	103,000,000
Total debt	100,990,000,000	98,693,000,000
Accrued interest included in fair value of debt	586,000,000	618,000,000
Fair value of debt	103,968,000,000	101,866,000,000
Fair value of short-term debt	10,500,000,000	9,700,000,000
Asset-backed commercial paper [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	0.20%	0.20%
Total short-term debt	1,331,000,000	3,364,000,000
Floating Rate Demand Notes [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	1.10%	1.10%
Total short-term debt	5,513,000,000	5,319,000,000
Other asset-backed short-term debt [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	0.70%	0.70%
Total short-term debt	1,972,000,000	1,963,000,000
Unsecured commercial paper [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	0.80%	0.90%
Total short-term debt	2,464,000,000	2,003,000,000
Other short-term debt [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	5.70%	5.30%
Total short-term debt	2,532,000,000	2,372,000,000
Total short-term debt [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	1.70%	1.50%
Average Effective (interest rate)	1.80%	1.50%
Total short-term debt	13,812,000,000	15,021,000,000
Senior indebtedness [Member]
Debt Instrument [Line Items]
Notes payable within one year	5,675,000,000	4,479,000,000
Notes payable after one year	39,533,000,000	38,617,000,000
Asset-backed debt [Member]
Debt Instrument [Line Items]
Notes payable within one year	17,409,000,000	17,322,000,000
Notes payable after one year	24,448,000,000	23,238,000,000
Total long-term debt [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	2.90%	3.00%
Average Effective (interest rate)	3.10%	3.20%
Total long-term debt	$ 87,178,000,000	$ 83,672,000,000