Postretirement Benefit Plans - Asset Allocation Range (Detail)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation	36.00%	37.00%
Minimum range	30.00%
Maximum range	40.00%
International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation	29.00%	30.00%
Minimum range	20.00%
Maximum range	40.00%
Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation	35.00%	32.00%
Minimum range	25.00%
Maximum range	45.00%
Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation	0.00%	1.00%
Minimum range	0.00%
Maximum range	5.00%

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Target allocation maximum percentage 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

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

+ References

+ Details

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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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