Shareholders' Equity (Share based Compensation Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 1,169	$ 854	$ 773
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	742	553	456
Restricted Stock And Performance Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	277	270	293
Equity Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 150	$ 31	$ 24