Stockholders' Deficit (Narrative) (Details) shares in Millions	3 Months Ended
	Apr. 30, 2019 $ / shares shares
Class of Stock [Line Items]
Common stock repurchased and retired (in shares)	0.6
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share) | $ / shares	$ 171.84
Common Stock Repurchase Program
Class of Stock [Line Items]
Common stock shares remained available for repurchase under repurchase plans (in shares)	16.8