Business And Chapter 11 Reorganization (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended		1 Months Ended		3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Aug. 31, 2009	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Business And Basis Of Presentation [Line Items]
Bankruptcy voluntary petition filed for relief date	Dec. 01, 2000
Bankruptcy court where petition filed	United States Bankruptcy Court for the District of Delaware
Plan of Reorganization approved date	Oct. 01, 2006
Entity arising from bankruptcy proceeding	Asbestos Personal Injury Settlement Trust ("Asbestos PI Trust")
Payment to acquire shares held in treasury		$ 261.4
Treasury shares acquired	5,057,382
Asbestos PI Trust [Member]
Business And Basis Of Presentation [Line Items]
Sale of stock by investee			1,845,023
Holding percentage in Armstrong World Industries, Inc.	17.00%				17.00%
Asbestos PI Trust And TPG [Member]
Business And Basis Of Presentation [Line Items]
Purchase of common stock by major shareholder				7,000,000
Sale of stock by investee			3,900,000		3,900,000	6,000,000	12,057,382	5,980,000
Armor TPG Holdings LLC [Member]
Business And Basis Of Presentation [Line Items]
Sale of stock by investee			2,054,977
Additional Economic Interest [Member] | Asbestos PI Trust And TPG [Member]
Business And Basis Of Presentation [Line Items]
Purchase of common stock by major shareholder				1,039,777