Health Care Trend Rate Assumption Effects (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Health Care Cost Trend Rates Assumptions [Line Items]
Effect on Postretirement Benefit Obligation - 1 Percentage Point Increase	$ 1.0
Effect on Total Service and Interest Cost Components - 1 Percentage Point Increase	0
Effect on Postretirement Benefit Obligation - 1 Percentage Point Decrease	(0.9)
Effect on Total Service and Interest Cost Components - 1 Percentage Point Decrease	$ 0

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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=35743120&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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