Retirement-Related Benefits (Schedule of Contribution Expense Related to Defined Contribution Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Contribution expense from retirement plans [Line Items]
Total contribution expense for defined contribution and benefit plans	$ 1,250	$ 1,237	$ 1,146
Domestic Plan [Member]
Contribution expense from retirement plans [Line Items]
Defined contribution plan, cost	1,124	1,064	967
Foreign Plan [Member]
Contribution expense from retirement plans [Line Items]
Defined contribution plan, cost	$ 126	$ 173	$ 179