Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions				1 Months Ended	3 Months Ended	9 Months Ended
	Nov. 05, 2015	Nov. 03, 2015	Nov. 02, 2015	Jan. 31, 2016	Jan. 03, 2016	Jan. 03, 2016	Oct. 29, 2015	Apr. 30, 2015
Class of Stock [Line Items]
Number of shares repurchased (shares)					10.7	14.5
Cost of shares repurchased					$ 267,200,000	$ 344,200,000
Amount available for future purchase					263,700,000	263,700,000
April 2015 Stock Repurchase Program
Class of Stock [Line Items]
Authorized amount								$ 300,000,000
Cost of shares repurchased					7,900,000
October 2015 Stock Repurchase Program
Class of Stock [Line Items]
Additional authorized repurchase amount							$ 300,000,000
Cost of shares repurchased		$ 300,000,000
Accelerated Share Repurchase Program
Class of Stock [Line Items]
Cost of shares repurchased		$ 225,000,000
November 2, 2015 | Accelerated Share Repurchase Program
Class of Stock [Line Items]
Number of shares repurchased (shares)	7.0
Cost of shares repurchased			$ 225,000,000
Accelerated share repurchases, prepayment for settlement					$ 45,000,000	$ 45,000,000
Subsequent event | November 2, 2015 | Accelerated Share Repurchase Program
Class of Stock [Line Items]
Number of shares repurchased (shares)				1.6
Accelerated share repurchases, average price per share (in usd per share)				$ 28.32