Weighted Average Assumptions Used to Determine Benefit Obligation (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.20%	4.90%
Rate of compensation increase		0.90%
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.90%	4.80%
Rate of compensation increase	3.60%	3.60%
Health care cost trend, Ultimate	5.80%	5.90%
Other Postretirement Benefit Plans, Defined Benefit | Pre Age Sixty Five
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend, Current	7.40%	7.00%
Other Postretirement Benefit Plans, Defined Benefit | Post Age Sixty Five
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend, Current	7.40%	7.00%