Price Risk Management Net volumes related to price risk management activities (Details) (CAD) In Millions, unless otherwise specified	Sep. 30, 2012 MMBTU MWh	Dec. 31, 2011 MWh MMBTU
Commodity contracts:
Electricity	10,000,000	13,000,000
Natural gas	85,000,000	79,000,000
Foreign currency	8	6

Aggregate notional amount of foreign currency exchange rate derivatives. Notional amount refers to the number of currency units specified in the foreign currency derivative contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

-URI http://asc.fasb.org/extlink&oid=6519104

Name:	us-gaap_NotionalAmountOfForeignCurrencyDerivatives
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant