Debt (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Unamortized discount	$ (37)	$ (51)
Adjustment Fair Value Hedging Instruments Unsecured Debt	735	428
Total debt	113,309	105,037
Fair value of debt	$ 114,187	$ 107,190
Average Contractual (interest rate)	2.20%	2.60%
Average Effective (interest rate)	2.30%	2.70%
Short Term Debt Carrying Value Fair Value	$ 9,800	$ 9,800
Floating Rate Demand Notes [Member]
Debt Instrument [Line Items]
Total short-term debt	5,854	5,559
Unsecured commercial paper [Member]
Debt Instrument [Line Items]
Total short-term debt	1,941	1,651
Other short-term debt [Member]
Debt Instrument [Line Items]
Total short-term debt	2,012	2,564
Asset-backed Securities [Member]
Debt Instrument [Line Items]
Total short-term debt	1,877	1,377
Notes payable within one year	18,462	16,722
Notes payable after one year	27,553	25,197
Total short-term debt [Member]
Debt Instrument [Line Items]
Total short-term debt	$ 11,684	$ 11,151
Average Contractual (interest rate)	1.50%	1.90%
Average Effective (interest rate)	1.50%	1.90%
Unsecured Debt [Member]
Debt Instrument [Line Items]
Notes payable within one year	$ 7,899	$ 9,102
Notes payable after one year	47,013	42,488
Total long-term debt [Member]
Debt Instrument [Line Items]
Long-term Debt and Capital Lease Obligations, Including Current Maturities	$ 101,625	$ 93,886
Average Contractual (interest rate)	2.30%	2.70%
Average Effective (interest rate)	2.40%	2.80%