Debt (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Average Contractual (interest rate)	3.30%	3.70%
Average Effective (interest rate)	3.50%	4.00%
Unamortized discount	$ (128,000,000)	$ (149,000,000)
Fair value adjustments	791,000,000	681,000,000
Total debt	89,258,000,000	84,659,000,000
Accrued interest included in fair value of debt	708,000,000	875,000,000
Fair value of debt	92,799,000,000	86,785,000,000
Fair value of short-term debt	8,000,000,000	6,400,000,000
Asset-backed commercial paper [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	0.40%	0.30%
Total short-term debt	5,752,000,000	6,835,000,000
Floating Rate Demand Notes [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	1.10%	1.30%
Total short-term debt	4,890,000,000	4,713,000,000
Other asset-backed short-term debt [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	1.10%	1.50%
Total short-term debt	3,616,000,000	2,741,000,000
Unsecured commercial paper [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	1.20%	5.40%
Total short-term debt	1,686,000,000	156,000,000
Other short-term debt [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	4.70%	7.00%
Total short-term debt	1,434,000,000	1,579,000,000
Total short-term debt [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	1.10%	1.40%
Average Effective (interest rate)	1.10%	1.40%
Total short-term debt	17,378,000,000	16,024,000,000
Senior indebtedness [Member]
Debt Instrument [Line Items]
Notes payable within one year	5,557,000,000	6,127,000,000
Notes payable after one year	31,656,000,000	24,892,000,000
Asset-backed debt [Member]
Debt Instrument [Line Items]
Notes payable within one year	13,788,000,000	16,526,000,000
Notes payable after one year	20,216,000,000	20,558,000,000
Total long-term debt [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	3.80%	4.20%
Average Effective (interest rate)	4.10%	4.60%
Total long-term debt	$ 71,880,000,000	$ 68,635,000,000