Financial Instruments and Fair Value Measurements - Quantitative Information About Level Three Fair Value Measurements (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Oct. 24, 2014
Fair Value Inputs, Assets, Quantitative Information [Line Items]
ARSs Fair Value	$ 2,649.2
Auction Rate Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
ARSs Fair Value	23.0
Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
ARSs Fair Value	23.0
Significant Unobservable Inputs (Level 3) | Auction Rate Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
ARSs Fair Value	$ 23.0
Minimum | Discounted Cash Flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Time-to-economic maturity	6 months
Illiquidity premium	1.20%
Coupon rate	1.20%
Minimum | Market Comparable Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	1.10%
Maximum | Discounted Cash Flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Time-to-economic maturity	9 years 3 months 18 days
Illiquidity premium	1.60%
Coupon rate	1.80%
Maximum | Market Comparable Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	2.30%
Weighted Average | Discounted Cash Flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Time-to-economic maturity	3 years 4 months 24 days
Illiquidity premium	1.30%
Coupon rate	1.40%
Weighted Average | Market Comparable Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	1.50%