Actual Allocation of the Assets in the Pension Plans (Detail) (Pension Plans, Defined Benefit)	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Total allocation of the assets	100.00%	100.00%
US Large Capitalization Equities
Defined Benefit Plan Disclosure [Line Items]
Actual allocation of the assets - equity securities	29.00%	39.00%
US Small Capitalization Equities
Defined Benefit Plan Disclosure [Line Items]
Actual allocation of the assets - equity securities	6.00%	9.00%
International Equities
Defined Benefit Plan Disclosure [Line Items]
Actual allocation of the assets - equity securities	7.00%	11.00%
US Long-Duration Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Actual allocation of the assets - debt securities	55.00%	0.00%
US Core Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Actual allocation of the assets - debt securities	0.00%	35.00%
High Yield Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Actual allocation of the assets - debt securities	3.00%	6.00%