Summary of Option Activity Under Stock Option Plans (Detail) (JPY ¥) In Millions, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2011 Year	Dec. 31, 2010 Year	Dec. 31, 2009 Year
Shares
Outstanding at beginning of year	2,220,000	1,512,000	592,000
Granted	912,000	890,000	954,000
Exercised	(65,800)
Forfeited	(24,000)	(182,000)	(34,000)
Outstanding at end of year	3,042,200	2,220,000	1,512,000
Exercisable at end of year	1,274,200
Weighted-Average Exercise Price
Outstanding at beginning of year	¥ 4,354	¥ 4,119	¥ 5,502
Granted	¥ 3,990	¥ 4,573	¥ 3,287
Exercised	¥ 3,287
Forfeited	¥ 4,282	¥ 3,479	¥ 4,851
Outstanding at end of year	¥ 4,268	¥ 4,354	¥ 4,119
Exercisable at end of year	¥ 4,257
Weighted-Average Remaining Contractual Term
Outstanding at beginning	2.5	3.0	3.3
Outstanding at end of year	2.0	2.5	3.0
Exercisable at end of year	0.9
Aggregate Intrinsic Value
Outstanding at end of year	¥ 88	¥ 722	¥ 588
Exercisable at end of year	¥ 88

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of vested portions of options outstanding and currently exercisable under the option plan as of the balance sheet date.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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The weighted average period between the balance sheet date and expiration for all vested portions of options outstanding and currently exercisable (or convertible) under the plan, which may be expressed in a decimal value for number of years.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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The weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated during the reporting period due to noncompliance with plan terms during the reporting period.

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Net number of share options (or share units) granted during the period.

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The weighted average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on stock options awarded under the plan during the reporting period.

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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The weighted average price as of the beginning of the year at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Number of share options (or share units) exercised during the current period.

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