Pensions and Other Postretirement Benefits - Summary of Key Actuarial Assumptions Used to Determine Net Periodic Pension and Other Retiree Benefit Credit or Expense (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined benefit pension plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Discount rate	4.00%	5.10%	5.60%
Expected return on plan assets	10.00%	10.00%	10.00%
Rate of compensation increase	3.60%	3.60%	3.60%
OPEB [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Discount rate	4.00%	5.00%	5.50%