Goodwill (Changes in the Carrying Amount of Goodwill) (Details)	3 Months Ended	6 Months Ended
Jul. 31, 2019 USD ($)	Jul. 31, 2019 USD ($) segment reporting_unit
Goodwill [Roll Forward]
Goodwill gross, beginning of the period		$ 2,600,000,000.0
Less: accumulated impairment losses, beginning of the period		(149,200,000)
Goodwill net, beginning of the period		2,450,800,000
Effect of foreign currency translation, measurement period adjustments, and other		(19,000,000.0)
Goodwill net, end of the period	$ 2,431,800,000	$ 2,431,800,000
Number of operating segments \| segment		1
Number of reporting units \| reporting_unit		1
Goodwill impairment loss	$ 0	$ 0

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount before accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of increase (decrease) from foreign currency translation adjustments and purchase accounting adjustments of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Number of reporting units tested for impairment of goodwill. A reporting unit is an operating segment or one level below an operating segment.

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