Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

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-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Name:	us-gaap_TreasuryStockValueAcquiredCostMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Stockholders' Equity - Share Repurchases (Details) - USD ($)	3 Months Ended		12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Oct. 31, 2019	Mar. 31, 2017	Dec. 31, 2011
Stockholders' Equity Note [Abstract]
Share repurchase program, authorized amount for repurchase				$ 1,000,000,000.0	$ 500,000,000.0
Share repurchase program, common stock repurchased (in shares)	0		537,000
Share repurchase program, common stock repurchased		$ 6,100,000	$ 156,100,000
Share repurchase program, remaining authorized amount for repurchase	$ 407,400,000