EARNINGS PER SHARE - Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings:
Net earnings	$ 77.9	$ 86.1
Earnings attributable to noncontrolling interest, net of tax	0.0	0.0
Net earnings from continuing operations attributable to Leggett & Platt, Inc. common shareholders	77.9	86.1
Earnings (loss) from discontinued operations, net of tax	0.0	0.0
Net earnings attributable to Leggett & Platt, Inc. common shareholders	$ 77.9	$ 86.1
Weighted average number of shares:
Weighted average number of common shares used in basic EPS (in shares)	135.3	136.8
Additional dilutive shares principally from the assumed exercise of outstanding stock options (in shares)	1.0	1.3
Weighted average number of common shares and dilutive potential common shares used in diluted EPS (in shares)	136.3	138.1
Basic EPS attributable to Leggett & Platt, Inc. common shareholders
Continuing operations (in dollars per share)	$ 0.58	$ 0.63
Discontinued operations (in dollars per share)	0.00	0.00
Basic (in dollars per share)	0.58	0.63
Diluted EPS attributable to Leggett & Platt, Inc. common shareholders
Continuing operations (in dollars per share)	0.57	0.62
Discontinued operations (in dollars per share)	0.00	0.00
Diluted (in dollars per share)	$ 0.57	$ 0.62
Other information:
Anti-dilutive shares excluded from diluted EPS computation (in shares)	0.1	0.0