Weighted Average Assumptions Used to Determine Net Periodic Benefit Cost (Detail)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Pension Plans, Defined Benefit
Schedule of Net Periodic Benefit Costs Weighted Average Assumptions [Line Items]
Discount rate	4.10%	4.70%	4.50%
Expected return on plan assets	4.80%	5.20%	5.20%
Rate of compensation increase	2.60%	2.70%	2.70%
Measurement Date	December 31, 2011	December 31, 2010	December 31, 2009
Other Postretirement Benefit Plans, Defined Benefit
Schedule of Net Periodic Benefit Costs Weighted Average Assumptions [Line Items]
Discount rate	5.00%	5.50%	6.30%
Health care cost trend	7.50%	8.00%	8.50%
Ultimate health care cost trend	5.00%	5.00%	5.00%
Years until ultimate trend is reached	6.0	7.0	8.0
Measurement Date	December 31, 2011	December 31, 2010	December 31, 2009