Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings:
Earnings from continuing operations	$ 86.9	$ 99.6	$ 86.3	$ 61.1	$ 53.1	$ 90.0	$ 85.1	$ 77.9	$ 333.9	$ 306.1	$ 293.6
(Earnings) attributable to noncontrolling interest, net of tax	(0.1)	0.0	(0.1)	0.1	(0.1)	0.0	(0.1)	0.0	(0.1)	(0.2)	(0.1)
Net earnings from continuing operations attributable to Leggett & Platt common shareholders									333.8	305.9	293.5
Earnings (loss) from discontinued operations, net of tax	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	(0.9)
Net earnings attributable to Leggett & Platt, Inc. common shareholders	$ 86.8	$ 99.6	$ 86.2	$ 61.2	$ 53.0	$ 90.0	$ 85.0	$ 77.9	$ 333.8	$ 305.9	$ 292.6
Weighted average number of shares (in millions):
Weighted average number of common shares used in basic EPS (in shares)									134.8	134.3	136.0
Dilutive effect of equity-based compensation (in shares)									0.6	0.9	1.3
Weighted average number of common shares and dilutive potential common shares used in diluted EPS (in shares)									135.4	135.2	137.3
Basic EPS attributable to Leggett & Platt common shareholders
Continuing operations (in dollars per share)	$ 0.64	$ 0.74	$ 0.64	$ 0.46	$ 0.40	$ 0.67	$ 0.63	$ 0.58	$ 2.48	$ 2.28	$ 2.16
Discontinued operations (in dollars per share)	0	0	0	0	0	0	0	0	0	0	(0.01)
Basic (in dollars per share)	0.64	0.74	0.64	0.46	0.40	0.67	0.63	0.58	2.48	2.28	2.15
Diluted EPS attributable to Leggett & Platt common shareholders
Continuing operations (in dollars per share)	0.64	0.74	0.64	0.45	0.39	0.67	0.63	0.57	2.47	2.26	2.14
Discontinued operations (in dollars per share)	0	0	0	0	0	0	0	0	0	0	(0.01)
Diluted (in dollars per share)	$ 0.64	$ 0.74	$ 0.64	$ 0.45	$ 0.39	$ 0.67	$ 0.63	$ 0.57	$ 2.47	$ 2.26	$ 2.13
Other information:
Anti-dilutive shares excluded from diluted EPS computation (in shares)									0.2	0.1	0.0
Cash dividends declared per share (in dollars per share)									$ 1.58	$ 1.50	$ 1.42