Stock-Based Compensation (Activities Related to Performance-based Stock Compensation) (Detail) - Performance-based stock compensation - ¥ / shares	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Stock Compensation Plan I
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, Granted during fiscal year	5,748,997	3,770,065
Number of shares, Vested during fiscal year	5,748,997	3,770,065
Weighted-average grant-date fair value, Granted during fiscal year	¥ 159.59	¥ 189.24
Weighted-average grant-date fair value, Vested during fiscal year	¥ 159.59	¥ 189.24
Stock Compensation Plan II
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested at the beginning of the year	15,157,092	13,319,406
Number of shares, Granted during fiscal year	3,281,003	6,906,635
Number of shares, Vested during fiscal year	7,014,809	5,068,949
Nonvested at the end of the year	11,423,286	15,157,092
Weighted-average grant-date fair value, Nonvested at the beginning of the year	¥ 183.50	¥ 182.04
Weighted-average grant-date fair value, Granted during fiscal year	159.59	189.24
Weighted-average grant-date fair value, Vested during fiscal year	182.07	187.48
Weighted-average grant-date fair value, Nonvested at the ending of the year	¥ 177.51	¥ 183.50

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(2)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(2)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of non-vested options outstanding.

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