Stock-Based Compensation Plans - Additional Information (Detail) - JPY (¥) ¥ / shares in Units, ¥ in Millions	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	¥ 5,958	¥ 5,499	¥ 5,249
Total cash received from exercise of stock acquisition rights plans	¥ 7,560	¥ 12,757	¥ 7,129
Stock Acquisition Rights Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation plan, vesting period	3 years
Weighted-average fair value per share of stock acquisition rights granted	¥ 1,864	¥ 1,593	¥ 2,045
Total intrinsic value of shares exercised under stock acquisition rights plan	¥ 7,575	¥ 13,325	¥ 6,970
Total unrecognized compensation expense	¥ 5,912
Total unrecognized compensation expense, weighted-average period to be recognized	1 year 11 months 19 days
Stock Acquisition Rights Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation plan, expiration period	10 years

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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