Pension Benefits - Plan Asset Allocations (Detail) (Pension benefits [Member])	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Equity Securities, Target Allocation, Minimum	55.00%
Equity Securities, Target Allocation, Maximum	65.00%
Debt Securities, Target Allocation, Minimum	27.00%
Debt Securities, Target Allocation, Maximum	33.00%
Real Estate, Target Allocation, Minimum	8.00%
Real Estate, Target Allocation, Maximum	12.00%
Plan Assets, Total	100.00%	100.00%	100.00%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets, Debt Securities	60.00%	61.00%	67.00%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets, Debt Securities	31.00%	32.00%	28.00%
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets, Debt Securities	9.00%	7.00%	5.00%

Defined Benefit Plan Target Allocation Percentage Of Assets Debt Securities Range Maximum1

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Defined Benefit Plan Target Allocation Percentage Of Assets Debt Securities Range Minimum 1

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Defined Benefit Plan Target Allocation Percentage Of Assets Equity Securities Range Maximum 1

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Defined Benefit Plan, Target Allocation Percentage, total

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

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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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