Calculation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Company Earnings Per Share [Line Items]
Earnings from continuing operations	$ 63.0	$ 55.5	$ 107.5	$ 101.8
(Earnings) loss attributable to noncontrolling interest, net of tax	(0.5)	(0.8)	(1.0)	(2.1)
Net earnings from continuing operations attributable to Leggett & Platt, Inc. common shareholders	62.5	54.7	106.5	99.7
Earnings from discontinued operations, net of tax	2.4		2.4
Net earnings attributable to Leggett & Platt, Inc. common shareholders	$ 64.9	$ 54.7	$ 108.9	$ 99.7
Weighted average number of common shares used in basic EPS	144.1	145.6	143.8	147.4
Additional dilutive shares principally from the assumed exercise of outstanding stock options	1.3	1.8	1.5	1.7
Weighted average number of common shares and dilutive potential common shares used in diluted EPS	145.4	147.4	145.3	149.1
Continuing operations	$ 0.43	$ 0.38	$ 0.74	$ 0.68
Discontinued operations	$ 0.02	$ 0.00	$ 0.02	$ 0.00
Basic EPS attributable to Leggett & Platt, Inc. common shareholders	$ 0.45	$ 0.38	$ 0.76	$ 0.68
Continuing operations	$ 0.43	$ 0.37	$ 0.73	$ 0.67
Discontinued operations	$ 0.02	$ 0.00	$ 0.02	$ 0.00
Diluted EPS attributable to Leggett & Platt, Inc. common shareholders	$ 0.45	$ 0.37	$ 0.75	$ 0.67
Shares issuable under employee and non-employee stock options	11.5	11.6	11.5	11.6
Anti-dilutive shares excluded from diluted EPS computation	3.3	1.7	3.0	2.0