Overview and Summary of Significant Accounting Policies - Narrative (Details) $ in Millions		3 Months Ended
		Apr. 30, 2020 USD ($) segment		May 19, 2020 USD ($)	Jan. 31, 2020 USD ($)	Nov. 01, 2019 USD ($)	Oct. 31, 2019 USD ($)	Apr. 30, 2019 USD ($)		Jan. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)
Accounting Policies [Abstract]
Number of new reportable segments | segment		4
Segment Reporting Information [Line Items]
Stockholders' equity		$ 16,258					$ 17,149
ROU Assets		1,032
Total lease liabilities		1,114
Subsequent Event | Cost optimization and prioritization plan
Segment Reporting Information [Line Items]
Expected gross savings				$ 1,000
Annualized net run-rate savings				800
Subsequent Event | Cost optimization and prioritization plan | Minimum
Segment Reporting Information [Line Items]
Expected cash funding				1,000
Subsequent Event | Cost optimization and prioritization plan | Maximum
Segment Reporting Information [Line Items]
Expected cash funding				$ 1,300
Cumulative Effect, Period of Adoption, Adjustment
Segment Reporting Information [Line Items]
Stockholders' equity	[1]	0
Accounting Standards Update 2016-02
Segment Reporting Information [Line Items]
ROU Assets						$ 1,000
Total lease liabilities						$ 1,100
Accumulated Other Comprehensive Loss
Segment Reporting Information [Line Items]
Stockholders' equity		(3,625)			$ (3,700)		(3,727)	$ (3,180)		$ (3,294)	$ (3,218)
Accumulated Other Comprehensive Loss | Cumulative Effect, Period of Adoption, Adjustment
Segment Reporting Information [Line Items]
Stockholders' equity	[1]	(43)
Accumulated Other Comprehensive Loss | Accounting Standards Update 2018-02 | Cumulative Effect, Period of Adoption, Adjustment
Segment Reporting Information [Line Items]
Stockholders' equity					43
Accumulated Deficit
Segment Reporting Information [Line Items]
Stockholders' equity		(8,385)			(7,411)		$ (7,632)	(7,765)		$ (8,034)	$ (5,899)
Accumulated Deficit | Cumulative Effect, Period of Adoption, Adjustment
Segment Reporting Information [Line Items]
Stockholders' equity		$ 43	[1]					$ (2,162)	[2]
Accumulated Deficit | Accounting Standards Update 2018-02 | Cumulative Effect, Period of Adoption, Adjustment
Segment Reporting Information [Line Items]
Stockholders' equity					$ (43)

[1] Represents the impact of the adoption of an accounting standard update that allows for the reclassification of stranded tax effects from accumulated other comprehensive loss to accumulated deficit.

[2] $2.3 billion was related to a reduction to retained earnings as a result of the adoption of an accounting standard update for Income Taxes and $143 million was related to an addition to retained earnings as a result of the adoption of the new revenue accounting standard.