Segment Information - Operating Results (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2016
Segment Reporting Information
Net revenue	$ 7,946	$ 7,764	$ 7,468	$ 7,674	$ 7,660	$ 7,501	$ 6,808	$ 6,902	$ 30,852	$ 28,871	$ 30,280
Segment earnings (loss) from operations	$ 684	$ 516	$ 397	$ 261	$ (224)	$ 201	$ 195	$ 453	1,858	625	3,903
Hybrid IT
Segment Reporting Information
Net revenue									24,285	22,740	23,954
Intelligent Edge
Segment Reporting Information
Net revenue									2,912	2,554	2,635
Financial Services
Segment Reporting Information
Net revenue									3,656	3,574	3,097
Corporate Investments
Segment Reporting Information
Net revenue									(1)	3	594
Intersegment Eliminations
Segment Reporting Information
Net revenue									780	945	1,280
Intersegment Eliminations | Hybrid IT
Segment Reporting Information
Net revenue									748	887	1,148
Intersegment Eliminations | Intelligent Edge
Segment Reporting Information
Net revenue									17	30	39
Intersegment Eliminations | Financial Services
Segment Reporting Information
Net revenue									15	28	93
Intersegment Eliminations | Corporate Investments
Segment Reporting Information
Net revenue									0	0	0
Operating segments
Segment Reporting Information
Net revenue									31,632	29,816	31,560
Segment earnings (loss) from operations									3,091	2,720	3,533
Operating segments | Hybrid IT
Segment Reporting Information
Net revenue									25,033	23,627	25,102
Segment earnings (loss) from operations									2,654	2,274	3,182
Operating segments | Intelligent Edge
Segment Reporting Information
Net revenue									2,929	2,584	2,674
Segment earnings (loss) from operations									237	253	74
Operating segments | Financial Services
Segment Reporting Information
Net revenue									3,671	3,602	3,190
Segment earnings (loss) from operations									290	299	338
Operating segments | Corporate Investments
Segment Reporting Information
Net revenue									(1)	3	594
Segment earnings (loss) from operations									$ (90)	$ (106)	$ (61)