Investments (Narrative) (Details)	Jun. 30, 2020	Dec. 31, 2016	May 31, 2016
Dow Corning Corporation [Member]
Equity Method Investment, Ownership Percentage		50.00%	50.00%
Pittsburgh Corning Corporation PCC [Member] | Asbestos Litigation [Member]
Equity Method Investment, Ownership Percentage		50.00%
HSG [Member]
Equity Method Investment, Ownership Percentage	50.00%
Hemlock Semiconductor LLC [Member]
Equity Method Investment, Ownership Percentage	49.90%	49.90%
Hemlock Semiconductor Operations LLC [Member]
Equity Method Investment, Ownership Percentage	40.25%	40.25%