Earnings Per Share and Equity - Summary of earnings per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Oct. 01, 2021	Oct. 02, 2020	Oct. 01, 2021	Oct. 02, 2020
Earnings Per Share [Abstract]
Net income attributable to ON Semiconductor Corporation	$ 309.7	$ 160.6	$ 583.7	$ 145.2
Basic weighted average shares of common stock outstanding (in shares)	430.6	410.8	423.8	410.5
Dilutive effect of share-based awards (in shares)	2.3	1.8	2.3	1.6
Dilutive effect of convertible notes and warrants (in shares)	7.8	5.7	17.0	2.3
Diluted weighted-average shares of common stock outstanding (in shares)	440.7	418.3	443.1	414.4
Net income per share of common stock attributable to ON Semiconductor Corporation:
Basic (in dollars per share)	$ 0.72	$ 0.39	$ 1.38	$ 0.35
Diluted (in dollars per share)	$ 0.70	$ 0.38	$ 1.32	$ 0.35