Revenue - Effects of Applying Topic 606 (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Current assets	$ 1,524.6				$ 1,766.5				$ 1,524.6	$ 1,766.5		$ 1,766.5
Net property, plant and equipment	728.5				663.9				728.5	663.9	$ 565.5	663.9
Other assets	1,128.9				1,120.4				1,128.9	1,120.4		1,121.1
TOTAL ASSETS	3,382.0				3,550.8				3,382.0	3,550.8	2,984.1	3,551.5
Other current liabilities	86.4				88.7				86.4	88.7		91.7
All other current liabilities	729.3								729.3			887.5
Long-term liabilities	1,408.7				1,383.8				1,408.7	1,383.8		1,383.8
Retained earnings	2,613.8				2,511.3				2,613.8	2,511.3		2,509.0
Other equity	(1,456.2)								(1,456.2)			(1,320.5)
TOTAL LIABILITIES AND EQUITY	3,382.0				3,550.8				3,382.0	3,550.8		3,551.5
Net sales	1,046.7	$ 1,091.5	$ 1,102.5	$ 1,028.8	984.5	$ 1,009.7	$ 989.3	$ 960.3	4,269.5	3,943.8	3,749.9
Cost of goods sold									3,380.8	3,061.4	2,848.2
Gross profit	213.2	227.1	231.0	217.4	208.5	216.5	230.7	226.7	888.7	882.4	901.7
Selling and administrative expenses									425.1	400.5	395.7
All other									26.7
Earnings from continuing operations before interest and income taxes									436.9	467.9	522.0
Net interest expense									52.5
Income taxes									78.3	138.4	120.0
(Earnings) attributable to noncontrolling interest, net of tax	0.1	$ 0.0	$ 0.1	$ 0.0	0.1	$ 0.0	$ 0.0	$ 0.0	0.2	0.1	0.4
Net earnings from continuing operations attributable to Leggett & Platt common shareholders									305.9	293.5	$ 366.7
Topic 606 Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Current assets	0.0								0.0			0.0
Net property, plant and equipment	0.0								0.0			0.0
Other assets	(0.7)								(0.7)			0.7
TOTAL ASSETS	(0.7)								(0.7)			0.7
Other current liabilities	(2.9)								(2.9)			3.0
All other current liabilities	0.0								0.0			0.0
Long-term liabilities	0.0								0.0			0.0
Retained earnings	2.2								2.2			(2.3)
Other equity	0.0								0.0			0.0
TOTAL LIABILITIES AND EQUITY	(0.7)								(0.7)			$ 0.7
Net sales									14.0
Cost of goods sold									13.6
Gross profit									0.4
Selling and administrative expenses									0.0
All other									0.0
Earnings from continuing operations before interest and income taxes									0.4
Net interest expense									0.0
Income taxes									0.1
(Earnings) attributable to noncontrolling interest, net of tax									0.0
Net earnings from continuing operations attributable to Leggett & Platt common shareholders									0.3
Amounts Without Adoption of Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Current assets	1,524.6				1,766.5				1,524.6	1,766.5
Net property, plant and equipment	728.5				663.9				728.5	663.9
Other assets	1,128.2								1,128.2
TOTAL ASSETS	3,381.3				3,550.8				3,381.3	3,550.8
Other current liabilities	83.5				88.7				83.5	88.7
All other current liabilities	729.3				887.5				729.3	887.5
Long-term liabilities	1,408.7				1,383.8				1,408.7	1,383.8
Retained earnings	2,616.0				2,511.3				2,616.0	2,511.3
Other equity	(1,456.2)				(1,320.5)				(1,456.2)	(1,320.5)
TOTAL LIABILITIES AND EQUITY	$ 3,381.3				$ 3,550.8				3,381.3	$ 3,550.8
Net sales									4,283.5
Cost of goods sold									3,394.4
Gross profit									889.1
Selling and administrative expenses									425.1
All other									26.7
Earnings from continuing operations before interest and income taxes									437.3
Net interest expense									52.5
Income taxes									78.4
(Earnings) attributable to noncontrolling interest, net of tax									(0.2)
Net earnings from continuing operations attributable to Leggett & Platt common shareholders									$ 306.2