Pension Plans (Fair Value of Pension Plan Assets by Asset Category) (Parenthetical) (Detail) - JPY (¥) ¥ in Millions	Mar. 31, 2022	Mar. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	¥ 978,033	¥ 887,764
Japanese Companies Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	¥ 22	¥ 22
Japanese Government Bond Securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets investment allocation in pooled funds	70.00%	70.00%
Japanese Municipal Bonds Securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets investment allocation in pooled funds		10.00%
Japanese Corporate Bonds Securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets investment allocation in pooled funds	30.00%	20.00%
Fair value of pension plan assets	¥ 37	¥ 51
Foreign Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets investment allocation in pooled funds	90.00%	90.00%
Foreign Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets investment allocation in pooled funds	10.00%	10.00%

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- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

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- Definition

Amount of investment in equity method investee and investment in and advance to affiliate.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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