INVENTORIES - Financial Statements (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Jan. 01, 2020
Inventory [Line Items]
Percentage of LIFO inventory					33.00%
Cost of goods sold	$ 1,063.1	$ 937.9	$ 2,966.8	$ 2,461.2
Net gain from sale of assets and businesses	(0.9)	(2.1)	(29.5)	(2.1)
EBIT	144.2	150.2	443.8	251.5
Income taxes	28.6	22.7	91.3	45.6
Net earnings	$ 97.2	$ 107.1	$ 297.0	$ 145.1
Net earnings per share attributable to Leggett & Platt, Inc. common shareholders:
Basic (in dollars per share)	$ 0.71	$ 0.79	$ 2.18	$ 1.07
Diluted (in dollars per share)	$ 0.71	$ 0.79	$ 2.17	$ 1.07
Inventories	$ 970.2		$ 970.2		$ 691.5
Deferred income taxes	219.7		219.7		205.4
Retained earnings	$ 2,924.8		2,924.8		2,797.2
Writedown of inventories			10.8	$ 9.4
Deferred income tax (benefit) expense			0.8	(12.5)
Other, net			2.3	13.1
Inventories			$ (278.3)	36.3
Change In Inventory Valuation
Inventory [Line Items]
Cost of goods sold		$ 937.9		2,461.2
Net gain from sale of assets and businesses				(2.1)
EBIT		150.2		251.5
Income taxes		22.7		45.6
Net earnings		$ 107.1		$ 145.1
Net earnings per share attributable to Leggett & Platt, Inc. common shareholders:
Basic (in dollars per share)		$ 0.79		$ 1.07
Diluted (in dollars per share)		$ 0.79		$ 1.07
Inventories					691.5
Deferred income taxes					205.4
Retained earnings					2,797.2
Writedown of inventories				$ 9.4
Deferred income tax (benefit) expense				(12.5)
Other, net				11.0
Inventories				36.3
Previously Reported | Change In Inventory Valuation
Inventory [Line Items]
Cost of goods sold		$ 940.8		2,462.3
Net gain from sale of assets and businesses				(2.5)
EBIT		147.3		250.8
Income taxes		22.0		45.5
Net earnings		$ 104.9		$ 144.5
Net earnings per share attributable to Leggett & Platt, Inc. common shareholders:
Basic (in dollars per share)		$ 0.77		$ 1.06
Diluted (in dollars per share)		$ 0.77		$ 1.06
Inventories					645.5
Deferred income taxes					194.2
Retained earnings					2,762.4
Writedown of inventories				$ 8.3
Deferred income tax (benefit) expense				(12.6)
Other, net				10.6
Inventories				38.5
Adjustment | Change In Inventory Valuation
Inventory [Line Items]
Cost of goods sold		$ (2.9)		(1.1)
Net gain from sale of assets and businesses				0.4
EBIT		2.9		0.7
Income taxes		0.7		0.1
Net earnings		$ 2.2		$ 0.6
Net earnings per share attributable to Leggett & Platt, Inc. common shareholders:
Basic (in dollars per share)		$ 0.02		$ 0.01
Diluted (in dollars per share)		$ 0.02		$ 0.01
Inventories					46.0
Deferred income taxes					11.2
Retained earnings					$ 34.8	$ 29.4
Writedown of inventories				$ 1.1
Deferred income tax (benefit) expense				0.1
Other, net				0.4
Inventories				$ (2.2)