Financial Instruments and Fair Value Measurements - Summary of Investments (Detail) (USD $) In Millions, unless otherwise specified	Apr. 25, 2014	Apr. 26, 2013
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	$ 2,888.7	$ 5,375.1
Gross unrealized gains	10.8	16.4
Gross unrealized losses	(1.5)	(3.3)
Estimated fair value	2,898.0	5,388.2
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	2,142.3	3,132.8
Gross unrealized gains	10.5	14.9
Gross unrealized losses	(0.5)	(0.6)
Estimated fair value	2,152.3	3,147.1
U.S. Treasury And Government Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	263.4	392.8
Gross unrealized gains	0.3	0.9
Gross unrealized losses	(0.1)	0
Estimated fair value	263.6	393.7
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	168.4	178.5
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	168.4	178.5
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	245.0	135.4
Gross unrealized gains	0	0.1
Gross unrealized losses	0	0
Estimated fair value	245.0	135.5
Money Market Funds
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	0	1,463.1
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	0	1,463.1
Auction Rate Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	36.9	44.2
Gross unrealized gains	0	0.5
Gross unrealized losses	(0.9)	(2.7)
Estimated fair value	36.0	42.0
Equity Funds
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	32.7	28.3
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	$ 32.7	$ 28.3