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Schedule of Asset Allocation (Detail)	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
U.S. Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	100.00%
Actual asset allocations	0.00%	100.00%
U.S. Pension Plans, Defined Benefit | Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	100.00%
Actual asset allocations	98.00%	95.00%
U.S. Pension Plans, Defined Benefit | Cash And Other
Defined Benefit Plan Disclosure [Line Items]
Actual asset allocations	2.00%	5.00%
Supplemental Executive Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	100.00%
Actual asset allocations	100.00%	100.00%
Supplemental Executive Retirement Plan | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	65.00%
Actual asset allocations	59.00%	58.00%
Supplemental Executive Retirement Plan | Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	35.00%
Actual asset allocations	37.00%	39.00%
Supplemental Executive Retirement Plan | Cash And Other
Defined Benefit Plan Disclosure [Line Items]
Actual asset allocations	4.00%	3.00%

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Target allocation of investments of this type to total plan assets presented on a weighted average basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)(i)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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