| Asset Allocation Ranges and Actual Allocation, CRIP (Detail) (Canadian Retirement Income Plan, or CRIP) | 12 Months Ended | |
|---|---|---|
| Dec. 31, 2012 | Dec. 31, 2011 | |
| Canadian Equities | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Range minimum | 25.00% | |
| Range maximum | 50.00% | |
| Actual | 35.60% | 34.80% | 
| U.S. Equities | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Range minimum | 0.00% | |
| Range maximum | 19.00% | |
| Actual | 0.00% | 5.20% | 
| International Equities | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Range minimum | 0.00% | |
| Range maximum | 19.00% | |
| Actual | 14.10% | 8.90% | 
| Fixed Income | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Range minimum | 30.00% | |
| Range maximum | 70.00% | |
| Actual | 49.90% | 50.50% | 
| Money Market | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Range minimum | 0.00% | |
| Range maximum | 10.00% | |
| Actual | 0.40% | 0.60% | 
| X | ||||||||||
| 
- Details 
 | 
| X | ||||||||||
| 
- Definition Target allocation maximum percentage of investments of this type to total plan assets presented on a weighted average basis. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Definition Target allocation minimum percentage of investments of this type to total plan assets presented on a weighted average basis. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Definition Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 |