Net Income per Share - Computation of Basic and Diluted Net Income Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 25, 2013	Jan. 27, 2012	Jan. 25, 2013	Jan. 27, 2012
Computation Of Earnings Per Share [Line Items]
Net income	$ 158.1	$ 119.6	$ 331.5	$ 424.7
Shares used in basic computation	359.5	360.3	362.5	364.0
Dilutive potential shares related to employee equity award plans	5.1	7.6	5.1	9.1
Dilutive impact of assumed conversion of Convertible Notes	0.1	5.8	0.5	9.3
Dilutive impact of warrants	0	0	0	2.7
Shares used in diluted computation	364.7	373.7	368.1	385.1
Basic	$ 0.44	$ 0.33	$ 0.91	$ 1.17
Diluted	$ 0.43	$ 0.32	$ 0.90	$ 1.10