Pension and Other Postretirement Benefits - Summary of Plan Asset Allocations (Detail)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Target Plan Asset Allocation, Other	68.00%
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets, Equity	28.00%	31.00%
Plan Assets, Fixed Income	65.00%	62.00%
Plan Assets, Other	7.00%	7.00%
Plan Assets, Total	100.00%	100.00%
Target Plan Asset Allocation, Equity	27.00%	28.00%
Target Plan Asset Allocation, Fixed Income	68.00%	66.00%
Target Plan Asset Allocation, Other	5.00%	6.00%
Target Plan Asset Allocation, Total	100.00%	100.00%
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets, Equity	64.00%	63.00%
Plan Assets, Fixed Income	34.00%	31.00%
Plan Assets, Cash	2.00%	6.00%
Plan Assets, Total	100.00%	100.00%
Target Plan Asset Allocation, Equity	60.00%	60.00%
Target Plan Asset Allocation, Fixed Income	35.00%	35.00%
Target Plan Asset Allocation, Cash	5.00%	5.00%
Target Plan Asset Allocation, Total	100.00%	100.00%

Defined benefit plan cash.

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- Definition

Defined benefit plan target allocation percentage one.

+ References

No definition available.

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- Definition

Defined benefit plan target allocation percentage of assets cash.

+ References

No definition available.

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- Definition

Defined benefit plan target allocation percentage of assets fixed income.

+ References

No definition available.

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- Definition

Defined benefit plan target allocation percent of assets equity securities.

+ References

No definition available.

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- Definition

Percentage of defined benefit plan fixed income assets.

+ References

No definition available.

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- Definition

Percentage of defined benefit plan other plan assets.

+ References

No definition available.

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- Definition

Percentage of defined benefits plan equity securities.

+ References

No definition available.

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- Definition

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 1

-Subparagraph (d)(i)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

Reference 2: 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=35743120&loc=d3e2446-114920

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- Definition

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=35743120&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=35743120&loc=d3e1928-114920

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