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Cash Equivalents and Investments - Textuals (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Investment
Dec. 31, 2013
Investment
Dec. 31, 2012
Cash Equivalents and Investments [Abstract]      
Total investments In unrealized loss position 437us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 178us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1  
Available-for-sale securities, gross realized gains $ 166.8us-gaap_AvailableForSaleSecuritiesGrossRealizedGains    
Privately-held investments 89.9jnpr_PrivatelyheldInvestments 57.2jnpr_PrivatelyheldInvestments  
Debt and redeemable preferred stock securities included in privately held investments 47.5us-gaap_CostMethodInvestments    
Unrealized gains, privately-held debt securities 15.0us-gaap_UnrealizedGainLossOnMarketableSecuritiesCostMethodInvestmentsAndOtherInvestments    
Unrealized gain on privately held investments   102.7jnpr_UnrealizedGainonCostMethodInvestmentsRecordedUponInvesteePublicOffering  
Other than temporary impairment of privately held equity investments $ 1.1us-gaap_CostmethodInvestmentsOtherThanTemporaryImpairment $ 2.8us-gaap_CostmethodInvestmentsOtherThanTemporaryImpairment $ 20.0us-gaap_CostmethodInvestmentsOtherThanTemporaryImpairment