Financial Instruments - Effect of Hedge Activity on Income and Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss)
Total amounts of income and expense line items	$ (1,136)	$ (1,424)
Cost of Services
Derivative Instruments, Gain (Loss)
Total amounts of income and expense line items	8,835
Gains/(losses) of total hedge activity	19
Cost of Sales
Derivative Instruments, Gain (Loss)
Total amounts of income and expense line items	1,722
Gains/(losses) of total hedge activity	(17)
Cost of Financing
Derivative Instruments, Gain (Loss)
Total amounts of income and expense line items	269
Gains/(losses) of total hedge activity	23
SG&A Expense
Derivative Instruments, Gain (Loss)
Total amounts of income and expense line items	5,445
Gains/(losses) of total hedge activity	(33)
Other (Income) and Expense
Derivative Instruments, Gain (Loss)
Total amounts of income and expense line items	413
Gains/(losses) of total hedge activity	49
Interest Expense
Derivative Instruments, Gain (Loss)
Total amounts of income and expense line items	165
Gains/(losses) of total hedge activity	$ (15)