Stockholders' Deficit (Narrative) (Details) shares in Millions	3 Months Ended	6 Months Ended
	Jul. 31, 2019 $ / shares shares	Jul. 31, 2019 $ / shares shares
Class of Stock [Line Items]
Common stock repurchased and retired (in shares)	0.3	0.9
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share) | $ / shares	$ 159.54	$ 168.11
Common Stock Repurchase Program
Class of Stock [Line Items]
Common stock shares remained available for repurchase under repurchase plans (in shares)	16.6	16.6