Komatsu Ltd. Shareholders' Equity [Details 1] In Thousands, except Share data, unless otherwise specified	12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended
Mar. 31, 2011 USD ($)	Mar. 31, 2011 JPY (¥)	Mar. 31, 2010 JPY (¥)	Mar. 31, 2009 JPY (¥)	Mar. 31, 2011 Range One [Member] JPY (¥)	Mar. 31, 2011 Range One [Member] USD ($)	Mar. 31, 2011 Range Two [Member] JPY (¥)	Mar. 31, 2011 Range Two [Member] USD ($)	Mar. 31, 2011 Range Three [Member] JPY (¥)	Mar. 31, 2011 Range Three [Member] USD ($)	Mar. 31, 2011 Range Four [Member] JPY (¥)	Mar. 31, 2011 Range Four [Member] USD ($)	Mar. 31, 2011 Range Five [Member] JPY (¥)	Mar. 31, 2011 Range Five [Member] USD ($)
Options outstanding and options exercisable
Exercise Prices, Lower Range		¥ 1			¥ 1		¥ 651		¥ 901		¥ 1,351		¥ 2,326
Exercise Prices, Upper Range		¥ 3,700			¥ 650		¥ 900		¥ 1,350		¥ 2,325		¥ 3,700
Options Outstanding, Number of shares	3,235,800	3,235,800				76,800		300,000		575,000		1,259,000		1,025,000
Options Outstanding, Weighted average exercise price	$ 24.66	¥ 2,047.00			¥ 1	$ 0.01	¥ 673.00	$ 8.11	¥ 1,126.00	$ 13.57	¥ 2,032.00	$ 24.48	¥ 3,136.00	$ 37.78
Options Outstanding, Intrinsic value	$ 36,000	¥ 2,988,000			¥ 216,000	$ 2,602	¥ 646,000	$ 7,783	¥ 977,000	$ 11,771	¥ 998,000	$ 12,025	¥ 151,000	$ 1,819
Options Outstanding, Weighted average remaining contractual life	4.1	4.1				7.3		1.3		2.3		4.8		4.9
Options Exercisable, Number of shares	3,159,000	3,159,000				0		330,000		575,000		1,259,000		1,025,000
Options Exercisable, Weighted average exercise price	$ 25.25	¥ 2,096.00			¥ 0	$ 0	¥ 673.00	$ 8.11	¥ 1,126.00	$ 13.57	¥ 2,032.00	$ 24.48	¥ 3,136.00	$ 37.78
Options Exercisable, Intrinsic value	$ 33,398	¥ 2,772,000			¥ 0	$ 0	¥ 646,000	$ 7,783	¥ 977,000	$ 11,771	¥ 998,000	$ 12,025	¥ 151,000	$ 1,819
Options Exercisable, Weighted average remaining contractual life	4.1	4.1				0		1.3		2.3		4.8		4.9
Risk-free rate of the share option
Grant-date fair value	$ 21.51	¥ 1,785.00	¥ 643.00	¥ 813.00
Expected term in Years	5	5	7	7
Risk-free rate, minimum	0.0013	0.0013	0.0017	0.006
Risk-free rate, maximum	0.0111	0.0111	0.0135	0.0148
Expected volatility	54.00%	54.00%	44.00%	39.00%
Expected dividend yield	0.96%	0.96%	2.07%	1.32%

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The period of time a share-based award is expected to be outstanding. A share-based award's expected term shall be determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior. An entity is required to aggregate individual awards into relatively homogeneous groups.

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The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance-sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.

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