Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Reconciliation of Cash, Cash Equivalents and Restricted Cash

The following table reconciles cash, cash equivalents and restricted cash as reported on the consolidated balance sheets to the aggregated amounts presented on the consolidated statements of cash flows:

December 31 (in millions)	2020		2019		2018
Cash and cash equivalents	$	207.3	$	21.0	$	44.9
Restricted cash		97.1		—		—
Total cash, cash equivalents and restricted cash    presented in the consolidated statements of cash flows	$	304.4	$	21.0	$	44.9

Estimated Service Lives for Property Plant and Equipment

The estimated service lives for property, plant and equipment are as follows:

Class of Assets	Range of Service Lives
Buildings	5 to 30 years
Machinery & Equipment	2 to 20 years
Land Improvements	5 to 60 years

Components of Changes in Accumulated Other Comprehensive Loss and Related Cumulative Noncurrent Deferred Tax Assets

The components of the changes in accumulated other comprehensive loss and related cumulative noncurrent deferred tax assets are as follows:

	Pension and Postretirement Benefit Plans			Foreign Currency			Unamortized Value of Terminated Forward Starting Interest Rate Swap			Total
years ended December 31 (in millions)	2020
Accumulated other comprehensive loss at beginning of    period	$	(144.9	)	$	(0.9	)	$	—		$	(145.8	)
Other comprehensive (loss) earnings before    reclassifications, net of tax		(26.6	)		0.6			—			(26.0	)
Amounts reclassified from accumulated other    comprehensive loss, net of tax		13.4			—			—			13.4
Other comprehensive (loss) earnings, net of tax		(13.2	)		0.6			—			(12.6	)
Accumulated other comprehensive loss at end of period	$	(158.1	)	$	(0.3	)	$	—		$	(158.4	)
Cumulative noncurrent deferred tax assets at end    of period	$	89.4		$	—		$	—		$	89.4
	2019
Accumulated other comprehensive loss at beginning of    period	$	(141.5	)	$	(2.1	)	$	—		$	(143.6	)
Other comprehensive (loss) earnings before    reclassifications, net of tax		(14.5	)		1.2			—			(13.3	)
Amounts reclassified from accumulated other    comprehensive loss, net of tax		11.1			—			—			11.1
Other comprehensive (loss) earnings, net of tax		(3.4	)		1.2			—			(2.2	)
Accumulated other comprehensive loss at end of period	$	(144.9	)	$	(0.9	)	$	—		$	(145.8	)
Cumulative noncurrent deferred tax assets at end    of period	$	85.2		$	—		$	—		$	85.2
	2018
Accumulated other comprehensive loss at beginning of    period	$	(128.8	)	$	—		$	(0.3	)	$	(129.1	)
Other comprehensive loss before reclassifications,    net of tax		(22.9	)		(2.1	)		—			(25.0	)
Amounts reclassified from accumulated other    comprehensive loss, net of tax		10.2			—			0.3			10.5
Other comprehensive (loss) earnings, net of tax		(12.7	)		(2.1	)		0.3			(14.5	)
Accumulated other comprehensive loss at end of period	$	(141.5	)	$	(2.1	)	$	—		$	(143.6	)
Cumulative noncurrent deferred tax assets at end    of period	$	84.2		$	—		$	—		$	84.2

Reclassification Out of Accumulated Other Comprehensive Loss

Reclassifications out of accumulated other comprehensive loss are as follows:

years ended December 31 (in millions)	2020			2019			2018			Affected line items in the consolidated statements of earnings
Pension and postretirement benefit plans:
Settlement charge	$	3.7		$	—		$	2.9
Amortization of:
Prior service credit		(0.1	)		(0.8	)		(2.0	)
Actuarial loss		14.3			15.5			12.7
		17.9			14.7			13.6		Other nonoperating (income)    and expenses, net
Tax effect		(4.5	)		(3.6	)		(3.4	)	Income tax expense
Total	$	13.4		$	11.1		$	10.2
Unamortized value of terminated forward starting    interest rate swap:
Additional interest expense	$	—		$	—		$	0.5		Interest expense
Tax effect		—			—			(0.2	)	Income tax expense
Total	$	—		$	—		$	0.3

Basic and Diluted Earnings Per Common Share

The following table reconciles the numerator and denominator for basic and diluted earnings per common share:

years ended December 31 (in millions)	2020		2019		2018
Net earnings attributable to Martin Marietta	$	721.0	$	611.9	$	470.0
Less:  distributed and undistributed earnings attributable to    unvested participating securities		0.6		0.9		0.8
Basic and diluted net earnings attributable to common    shareholders attributable to Martin Marietta	$	720.4	$	611.0	$	469.2
Basic weighted-average common shares outstanding		62.3		62.5		62.9
Effect of dilutive employee and director awards		0.1		0.2		0.2
Diluted weighted-average common shares outstanding		62.4		62.7		63.1