TCN Plan's Asset Allocations by Asset Category (Detail) (TCN Plan)	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations, by asset category	100.00%	100.00%
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations, by asset category	70.00%	70.00%
Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations, by asset category	30.00%	30.00%

The aggregate percentage of the fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of total plan assets held as of the measurement date.

Reference 1: 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e2446-114920

Reference 3: 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=6962843&loc=d3e1928-114920

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