Retirement-Related Benefits - All Retirement Plans Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Retirement-Related Benefits:
Defined benefit and contribution pension plans - cost	$ 664	$ 439
Nonpension postretirement plans - cost	61	60
Total	$ 725	$ 499
Year-to-year percent change, defined benefit and contribution pension plans cost (as a percent)	51.30%
Year-to-year percent change, nonpension postretirement plans cost (as a percent)	2.30%
Year-to-year percent change, total (as a percent)	45.40%