Accounting Policies - Basic and Diluted Earnings from Continuing Operations Per Common Share (Detail) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net earnings from continuing operations attributable to Martin Marietta	$ 702.0	$ 721.0	$ 611.9
Less: distributed and undistributed earnings attributable to unvested participating securities	0.2	0.6	0.9
Basic and diluted net earnings from continuing operations attributable to common shareholders attributable to Martin Marietta	$ 701.8	$ 720.4	$ 611.0
Basic weighted-average common shares outstanding	62.4	62.3	62.5
Effect of dilutive employee and director awards	0.2	0.1	0.2
Diluted weighted-average common shares outstanding	62.6	62.4	62.7