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Financing Arrangements - Carrying Value of Long-Term Debt (Detail) (USD $)
In Millions, unless otherwise specified
Apr. 24, 2015
Apr. 25, 2014
Debt Instrument [Line Items]    
Total principal amount $ 1,500.0us-gaap_DebtInstrumentFaceAmount $ 1,000.0us-gaap_DebtInstrumentFaceAmount
Less: Unamortized discount (5.0)us-gaap_DebtInstrumentUnamortizedDiscount (4.5)us-gaap_DebtInstrumentUnamortizedDiscount
Unamortized issuance costs (7.5)ntap_UnamortizedDebtIssuanceExpense1 (5.4)ntap_UnamortizedDebtIssuanceExpense1
Total long-term debt 1,487.5us-gaap_LongTermDebtNoncurrent 990.1us-gaap_LongTermDebtNoncurrent
Senior Notes | Due 2017    
Debt Instrument [Line Items]    
Total principal amount 750.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
750.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
Debt Instrument, Effective Interest Rate 2.25%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
2.25%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
Senior Notes | Due 2021    
Debt Instrument [Line Items]    
Total principal amount 500.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
Debt Instrument, Effective Interest Rate 3.54%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
 
Senior Notes | Due 2022    
Debt Instrument [Line Items]    
Total principal amount $ 250.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodThreeMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
$ 250.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodThreeMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
Debt Instrument, Effective Interest Rate 3.43%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodThreeMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
3.43%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodThreeMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember