EARNINGS PER SHARE - Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings:
Earnings from continuing operations	$ 90.0	$ 83.5	$ 253.0	$ 257.2
Earnings attributable to noncontrolling interest, net of tax	0.0	0.0	(0.1)	0.0
Net earnings from continuing operations attributable to Leggett & Platt, Inc. common shareholders	90.0	83.5	252.9	257.2
Earnings from discontinued operations, net of tax	0.0	(0.9)	0.0	(0.9)
Net earnings attributable to Leggett & Platt, Inc. common shareholders	$ 90.0	$ 82.6	$ 252.9	$ 256.3
Weighted average number of shares:
Weighted average number of common shares used in basic EPS (in shares)	133.8	135.7	134.4	136.1
Dilutive effect of stock-based compensation (in shares)	0.9	1.2	1.0	1.4
Weighted average number of common shares and dilutive potential common shares used in diluted EPS (in shares)	134.7	136.9	135.4	137.5
Basic EPS attributable to Leggett & Platt, Inc. common shareholders
Continuing operations (in dollars per share)	$ 0.67	$ 0.62	$ 1.88	$ 1.89
Discontinued operations (in dollars per share)	0.00	(0.01)	0.00	(0.01)
Basic (in dollars per share)	0.67	0.61	1.88	1.88
Diluted EPS attributable to Leggett & Platt, Inc. common shareholders
Continuing operations (in dollars per share)	0.67	0.61	1.87	1.87
Discontinued operations (in dollars per share)	0.00	(0.01)	0.00	(0.01)
Diluted (in dollars per share)	$ 0.67	$ 0.60	$ 1.87	$ 1.86
Other information:
Anti-dilutive shares excluded from diluted EPS computation (in shares)	0.0	0.1	0.1	0.0
Cash dividends declared per share (in dollars per share)	$ 0.38	$ 0.36	$ 1.12	$ 1.06