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Goodwill and Intangible Assets (Summary of Changes in Goodwill) (Details) (USD $)
In Millions, unless otherwise specified
Apr. 03, 2015
Dec. 31, 2014
Goodwill [Line Items]    
Goodwill $ 711.3us-gaap_GoodwillGross $ 711.3us-gaap_GoodwillGross
Accumulated Impairment Losses (447.5)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss (447.5)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
Carrying Value 263.8us-gaap_Goodwill 263.8us-gaap_Goodwill
Automotive Industrial Medical And Mil Aero [Member]    
Goodwill [Line Items]    
Goodwill 539.9us-gaap_GoodwillGross
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_AutomotiveIndustrialMedicalAndMilAeroMember
539.9us-gaap_GoodwillGross
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_AutomotiveIndustrialMedicalAndMilAeroMember
Accumulated Impairment Losses (418.9)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_AutomotiveIndustrialMedicalAndMilAeroMember
(418.9)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_AutomotiveIndustrialMedicalAndMilAeroMember
Carrying Value 121.0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_AutomotiveIndustrialMedicalAndMilAeroMember
121.0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_AutomotiveIndustrialMedicalAndMilAeroMember
Standard Products [Member]    
Goodwill [Line Items]    
Goodwill 76.0us-gaap_GoodwillGross
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_StandardProductsMember
76.0us-gaap_GoodwillGross
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_StandardProductsMember
Accumulated Impairment Losses (28.6)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_StandardProductsMember
(28.6)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_StandardProductsMember
Carrying Value 47.4us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_StandardProductsMember
47.4us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_StandardProductsMember
Computing And Consumer Products [Member]    
Goodwill [Line Items]    
Goodwill 95.4us-gaap_GoodwillGross
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_ComputingAndConsumerProductsMember
95.4us-gaap_GoodwillGross
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_ComputingAndConsumerProductsMember
Accumulated Impairment Losses 0us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_ComputingAndConsumerProductsMember
0us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_ComputingAndConsumerProductsMember
Carrying Value $ 95.4us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_ComputingAndConsumerProductsMember
$ 95.4us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= onnn_ComputingAndConsumerProductsMember