Retirement-Related Benefits - All Retirement Plans Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Retirement-Related Benefits:
Defined benefit and contribution pension plans - cost	$ 659	$ 455	$ 1,323	$ 894
Nonpension postretirement plans - cost	60	61	121	121
Total	$ 719	$ 516	$ 1,444	$ 1,014
Year-to-year percent change, defined benefit and contribution pension plans cost (as a percent)	44.90%		48.00%
Year-to-year percent change, nonpension postretirement plans cost (as a percent)	(0.90%)		0.70%
Year-to-year percent change, total (as a percent)	39.50%		42.40%