Stockholders' Deficit (Narrative) (Details) shares in Millions	3 Months Ended	9 Months Ended
	Oct. 31, 2019 $ / shares shares	Oct. 31, 2019 $ / shares shares
Class of Stock [Line Items]
Common stock repurchased and retired (in shares)	0.8	1.7
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share) | $ / shares	$ 144.49	$ 156.16
Common Stock Repurchase Program
Class of Stock [Line Items]
Common stock shares remained available for repurchase under repurchase plans (in shares)	15.7	15.7