Financial Instruments and Fair Value Measurements - Summary of Investments (Detail) (USD $) In Millions, unless otherwise specified	Jan. 23, 2015	Apr. 25, 2014
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	$ 3,008.7	$ 2,888.7
Gross unrealized gains	8.0	10.8
Gross unrealized losses	(0.5)	(1.5)
Estimated fair value	3,016.2us-gaap_AvailableForSaleSecurities	2,898.0us-gaap_AvailableForSaleSecurities
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	2,083.9	2,142.3
Gross unrealized gains	6.6	10.5
Gross unrealized losses	(0.4)	(0.5)
Estimated fair value	2,090.1	2,152.3
U.S. Treasury and Government Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	521.4	263.4
Gross unrealized gains	1.4	0.3
Gross unrealized losses	(0.1)	(0.1)
Estimated fair value	522.7	263.6
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	15.0	168.4
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	15.0	168.4
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	358.0	245.0
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	358.0	245.0
Auction Rate Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	0	36.9
Gross unrealized gains	0	0
Gross unrealized losses	0	(0.9)
Estimated fair value	0	36.0
Equity Funds
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	30.4	32.7
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	$ 30.4	$ 32.7

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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