Earnings Per Share and Equity - Summary of earnings per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jul. 03, 2020	Jun. 28, 2019	Jul. 03, 2020	Jun. 28, 2019
Earnings Per Share [Abstract]
Net income (loss) attributable to ON Semiconductor Corporation	$ (1.4)	$ 101.8	$ (15.4)	$ 215.9
Basic weighted average shares of common stock outstanding (in shares)	410.1	411.9	410.3	411.3
Dilutive effect of share-based awards (in shares)	0.0	1.9	0.0	2.6
Dilutive effect of convertible notes (in shares)	0.0	3.9	0.0	3.9
Diluted weighted-average shares of common stock outstanding (in shares)	410.1	417.7	410.3	417.8
Net income (loss) per share of common stock attributable to ON Semiconductor Corporation:
Basic (in dollars per share)	$ (0.00)	$ 0.25	$ (0.04)	$ 0.52
Diluted (in dollars per share)	$ (0.00)	$ 0.24	$ (0.04)	$ 0.52