Restructuring and Other Items, net (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 28, 2020 USD ($) Mill	Jun. 30, 2019 USD ($)	Jun. 28, 2020 USD ($) Mill	Jun. 30, 2019 USD ($)
Restructuring Charges [Abstract]
Impairment of assets	$ 6.0	$ 7.5	$ 6.0	$ 7.5
Severance and other employee costs	0.3	5.7	0.3	5.7
Total restructuring and other items, net	6.5	13.2	6.5	13.2
Restructuring Reserve [Roll Forward]
Restructuring liability, beginning of period			5.0
Additional provision			0.3
Cash payments			(0.7)
Restructuring liability, ending of period	4.6		4.6
Performance Materials [Member]
Restructuring Charges [Abstract]
Impairment of assets	0.0	4.2	0.0	4.2
Severance and other employee costs	0.0	2.8	0.0	2.8
Specialty Minerals [Member]
Restructuring Charges [Abstract]
Impairment of assets	6.0	1.6	6.0	1.6
Severance and other employee costs	0.3	0.9	0.3	0.9
Refractories [Member]
Restructuring Charges [Abstract]
Severance and other employee costs	0.0	0.8	0.0	0.8
Energy Services [Member]
Restructuring Charges [Abstract]
Impairment of assets	0.0	1.7	0.0	1.7
Severance and other employee costs	0.0	0.1	0.0	0.1
Corporate [Member]
Restructuring Charges [Abstract]
Severance and other employee costs	0.0	1.1	0.0	1.1
Other	$ 0.2	$ 0.0	$ 0.2	$ 0.0
Verso Papers [Member]
Restructuring and Other Items, Net [Abstract]
Number of paper mills being idled indefinitely | Mill	2		2