Debt (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Unamortized discount	$ (41)	$ (51)
Adjustment Fair Value Hedging Instruments Unsecured Debt	381	428
Total debt	109,521	105,037
Fair value of debt	$ 111,119	$ 107,190
Average Contractual (interest rate)	2.30%	2.60%
Average Effective (interest rate)	2.40%	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	5,651	5,559
Unsecured commercial paper [Member]
Debt Instrument [Line Items]
Total short-term debt	1,813	1,651
Other short-term debt [Member]
Debt Instrument [Line Items]
Total short-term debt	2,370	2,564
Asset-backed Securities [Member]
Debt Instrument [Line Items]
Total short-term debt	1,583	1,377
Notes payable within one year	17,354	16,722
Notes payable after one year	27,591	25,197
Total short-term debt [Member]
Debt Instrument [Line Items]
Total short-term debt	$ 11,417	$ 11,151
Average Contractual (interest rate)	1.70%	1.90%
Average Effective (interest rate)	1.80%	1.90%
Unsecured Debt [Member]
Debt Instrument [Line Items]
Notes payable within one year	$ 8,581	$ 9,102
Notes payable after one year	44,238	42,488
Total long-term debt [Member]
Debt Instrument [Line Items]
Long-term Debt and Capital Lease Obligations, Including Current Maturities	$ 98,104	$ 93,886
Average Contractual (interest rate)	2.40%	2.70%
Average Effective (interest rate)	2.50%	2.80%