Financial Instruments and Fair Value Measurements - Summary of Investments (Detail) (USD $) In Millions, unless otherwise specified	Oct. 24, 2014	Apr. 25, 2014
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	$ 2,636.9	$ 2,888.7
Gross unrealized gains	8.7	10.8
Gross unrealized losses	(0.5)	(1.5)
Estimated fair value	2,645.1	2,898.0
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	1,855.4	2,142.3
Gross unrealized gains	8.1	10.5
Gross unrealized losses	(0.2)	(0.5)
Estimated fair value	1,863.3	2,152.3
U.S. Treasury And Government Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	157.0	263.4
Gross unrealized gains	0.6	0.3
Gross unrealized losses	0	(0.1)
Estimated fair value	157.6	263.6
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	222.6	168.4
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	222.6	168.4
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	345.6	245.0
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	345.6	245.0
Auction Rate Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	23.3	36.9
Gross unrealized gains	0	0
Gross unrealized losses	(0.3)	(0.9)
Estimated fair value	23.0	36.0
Equity Funds
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	33.0	32.7
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	$ 33.0	$ 32.7