Earnings Per Share and Equity - Summary of earnings per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Apr. 03, 2020	Mar. 29, 2019
Earnings Per Share [Abstract]
Net income (loss) attributable to ON Semiconductor Corporation	$ (14.0)	$ 114.1
Basic weighted average common shares outstanding (in shares)	410.6	410.6
Dilutive effect of share-based awards (in shares)	0.0	3.2
Dilutive effect of convertible notes (in shares)	0.0	3.9
Diluted weighted average common shares outstanding (in shares)	410.6	417.7
Net income (loss) per common share attributable to ON Semiconductor Corporation:
Basic (in dollars per share)	$ (0.03)	$ 0.28
Diluted (in dollars per share)	$ (0.03)	$ 0.27