One-Percentage Rate Change in Assumed Health Care Cost Trend Rates and Its Effects on Accumulated Postretirement Benefit Obligation (Detail) $ in Thousands	12 Months Ended
Mar. 31, 2017 USD ($)
Compensation And Retirement Disclosure [Abstract]
Defined benefit plan, effect of one percentage point increase on accumulated postretirement benefit obligation	$ 215,686
Defined benefit plan, effect of one percentage point increase on aggregate service and interest cost	15,486
Defined benefit plan, effect of one percentage point decrease on accumulated postretirement benefit obligation	(195,172)
Defined benefit plan, effect of one percentage point decrease on aggregate service and interest cost	$ (13,842)

No definition available.

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- Definition

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

+ References

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

+ Details

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- Definition

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

+ References

+ Details

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- Definition

The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

+ References

+ Details

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- Definition

The effect of a one-percentage-point increase in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

+ References

+ Details

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