Retirement-Related Benefits - All Retirement Plans Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Retirement-Related Benefits:
Defined benefit and contribution pension plans - cost	$ 592	$ 421	$ 1,915	$ 1,315
Nonpension postretirement plans - cost	61	64	182	185
Total	$ 653	$ 486	$ 2,097	$ 1,500
Year-to-year percent change, defined benefit and contribution pension plans cost (as a percent)	40.60%		45.60%
Year-to-year percent change, nonpension postretirement plans cost (as a percent)	(5.90%)		(1.60%)
Year-to-year percent change, total (as a percent)	34.40%		39.80%