Postretirement Benefit Plans - Asset Allocation Range (Detail)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation	35.00%	33.00%
Minimum range	30.00%	30.00%
Maximum range	40.00%	40.00%
International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation	29.00%	27.00%
Minimum range	20.00%	20.00%
Maximum range	40.00%	40.00%
Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation	35.00%	35.00%
Minimum range	25.00%	25.00%
Maximum range	45.00%	45.00%
Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation	1.00%	5.00%
Minimum range	0.00%	0.00%
Maximum range	5.00%	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=21915506&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=21915506&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=21915506&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=21915506&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph d(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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