Debt (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total short-term debt	$ 16,207	$ 15,359
Unamortized discount	(7)	(8)
Unamortized issuance costs	(224)	(212)
Fair value adjustments	184	278
Total long-term debt	113,003	111,133
Total debt	$ 129,210	$ 126,492
Average Contractual (interest rate)	2.40%	2.40%
Average Effective (interest rate)	2.50%	2.40%
Short Term Debt Carrying Value Fair Value	$ 15,600	$ 14,300
Floating Rate Demand Notes [Member]
Debt Instrument [Line Items]
Total short-term debt	6,147	5,986
Unsecured commercial paper [Member]
Debt Instrument [Line Items]
Total short-term debt	4,986	4,507
Other short-term debt [Member]
Debt Instrument [Line Items]
Total short-term debt	4,498	3,803
Asset-backed Securities [Member]
Debt Instrument [Line Items]
Total short-term debt	576	1,063
Notes payable within one year	18,228	19,286
Notes payable after one year	$ 30,155	$ 30,112
Total short-term debt [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	2.30%	2.30%
Average Effective (interest rate)	2.30%	2.30%
Unsecured Debt [Member]
Debt Instrument [Line Items]
Notes payable within one year	$ 11,777	$ 12,369
Notes payable after one year	$ 52,890	$ 49,308
Total long-term debt [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	2.40%	2.40%
Average Effective (interest rate)	2.50%	2.50%
Level 2 [Member] | Fair Value, Measurements, Nonrecurring [Member]
Debt Instrument [Line Items]
Fair value of debt	$ 131,748	$ 128,001