Debt (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total short-term debt	$ 17,692	$ 15,359
Unamortized discount	(1)	(8)
Unamortized issuance costs	(223)	(212)
Fair value adjustments	162	278
Total long-term debt	114,688	111,133
Total debt	$ 132,380	$ 126,492
Average Contractual (interest rate)	2.50%	2.40%
Average Effective (interest rate)	2.50%	2.40%
Short Term Debt Carrying Value Fair Value	$ 16,500	$ 14,300
Floating Rate Demand Notes [Member]
Debt Instrument [Line Items]
Total short-term debt	5,718	5,986
Unsecured commercial paper [Member]
Debt Instrument [Line Items]
Total short-term debt	5,627	4,507
Other short-term debt [Member]
Debt Instrument [Line Items]
Total short-term debt	5,196	3,803
Asset-backed Securities [Member]
Debt Instrument [Line Items]
Total short-term debt	1,151	1,063
Notes payable within one year	16,496	19,286
Notes payable after one year	$ 30,909	$ 30,112
Total short-term debt [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	2.60%	2.30%
Average Effective (interest rate)	2.60%	2.30%
Unsecured Debt [Member]
Debt Instrument [Line Items]
Notes payable within one year	$ 13,487	$ 12,369
Notes payable after one year	$ 53,858	$ 49,308
Total long-term debt [Member]
Debt Instrument [Line Items]
Average Contractual (interest rate)	2.50%	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	$ 134,141	$ 128,001