Acquisitions (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			0 Months Ended	5 Months Ended	8 Months Ended	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Aug. 15, 2014	Dec. 31, 2014	Dec. 31, 2014	Apr. 30, 2014
Business Acquisition [Line Items]
Increase in acquisition costs	$ 8.1
Amount of non-controlling interest acquired in the period	10.00%				10.00%	10.00%
Goodwill	264.7	184.6			264.7	264.7
Amortization of acquisition-related intangible assets	68.4	33.1	44.4
Restructuring Costs	28.1	67.3	73.4
Aptima [Member]
Business Acquisition [Line Items]
Amount of non-controlling interest acquired in the period				100.00%
Purchase price				405.4
Business Combination, Consideration Withheld and Placed in Escrow	40.0			40.0	40.0	40.0
Revenues	209.0
Net income (loss) attributable to ON Semiconductor Corporation					(39.2)
Expensing of the acquisition related inventory step-up					22.3
Inventories after related step-up	25.5			84.8	25.5	25.5
In-process research and development				51.3
Intangible assets				206.9
Goodwill				65.3
Aptima [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Intangible assets				127.5
Weighted average useful life				2 years
Aptima [Member] | Developed Technology [Member]
Business Acquisition [Line Items]
Intangible assets				77.1
Aptima [Member] | Patents [Member]
Business Acquisition [Line Items]
Weighted average useful life				6 years
Aptima [Member] | Trademarks [Member]
Business Acquisition [Line Items]
Intangible assets				2.3
Weighted average useful life				6 months
Aptima [Member] | Scenario, Previously Reported [Member]
Business Acquisition [Line Items]
Inventories after related step-up				85.3
In-process research and development				75.4
Intangible assets				183.1
Goodwill				63.8
Truesense Imaging, Inc. [Member]
Business Acquisition [Line Items]
Amount of non-controlling interest acquired in the period							100.00%
Business Combination, Consideration, Liability	2.9				2.9	2.9
Revenues	53.4
Net income (loss) attributable to ON Semiconductor Corporation	(0.3)
Expensing of the acquisition related inventory step-up						4.7
Inventories after related step-up	10.4				10.4	10.4	18.3
In-process research and development							10.2
Intangible assets							35.5
Goodwill							23.5
Goodwill, tax deductible amount	2.0				2.0	2.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net							95.7
Truesense Imaging, Inc. [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Intangible assets							18.8
Weighted average useful life							5 years
Truesense Imaging, Inc. [Member] | Developed Technology [Member]
Business Acquisition [Line Items]
Intangible assets							16.7
Weighted average useful life							9 years
Truesense Imaging, Inc. [Member] | Scenario, Previously Reported [Member]
Business Acquisition [Line Items]
Inventories after related step-up							18.8
In-process research and development							7.5
Intangible assets							33.1
Goodwill							27.0
Truesense Imaging, Inc. [Member] | Scenario, Actual [Member]
Business Acquisition [Line Items]
Goodwill	23.5				23.5	23.5	23.5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles							35.5
Business Acquisitions [Member]
Business Acquisition [Line Items]
Amortization of acquisition-related intangible assets	50.8	95.4
Cost of Revenue [Member]
Business Acquisition [Line Items]
Expensing of the acquisition related inventory step-up	$ 27.0