Segment Results (Schedule of Segment Operating Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Total Consolidated Operating Income (Loss)	$ 70.2	$ 63.2
Mineral Fiber [Member]
Segment Reporting Information [Line Items]
Total Consolidated Operating Income (Loss)	63.8	57.6
Architectural Specialties [Member]
Segment Reporting Information [Line Items]
Total Consolidated Operating Income (Loss)	7.2	6.5
Unallocated Corporate [Member]
Segment Reporting Information [Line Items]
Total Consolidated Operating Income (Loss)	$ (0.8)	$ (0.9)