| Weighted-Average Assumptions used to Determine Benefit Obligations (Detail) | Dec. 31, 2012 | Dec. 31, 2011 | 
|---|---|---|
| Pension Benefits | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Discount rate | 4.17% | 4.60% | 
| Rate of compensation increase | 3.56% | 4.41% | 
| Other Benefits | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Discount rate | 4.03% | 4.29% | 
| Rate of compensation increase | 
| X | ||||||||||
| 
- Definition The interest rate used to adjust for the time value of money for the plan. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Definition Expected rate of compensation increases (for pay-related plans). Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Details 
 |