Financial and capital management - Equity price exposures (Details) - Equity price risk - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Disclosure of detailed information about hedging instruments [line items]
Percentage of possible change in risk variable	5.00%
Interest rate exposure, interest rate percent decrease	5.00%
Reasonably possible change in risk variable impact on net earnings	$ 38
Forward contract \| Settlement of share-based compensation plans
Disclosure of detailed information about hedging instruments [line items]
Financial instruments designated as hedging instruments, at fair value	$ 45	$ 111

The fair value of financial instruments designated as hedging instruments. Hedging instruments are designated derivatives or (for a hedge of the risk of changes in foreign currency exchange rates only) designated non-derivative financial assets or non-derivative financial liabilities whose fair value or cash flows are expected to offset changes in the fair value or cash flows of a designated hedged item. [Refer: At fair value [member]; Derivatives [member]; Derivative financial assets; Derivative financial liabilities; Financial instruments, class [member]; Financial assets; Financial liabilities]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2018-01-01
-Name IFRS
-Number 7
-IssueDate 2017-01-01
-Paragraph 22
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_22_b&doctype=Standard&book=B
-URIDate 2017-03-09

Name:	ifrs-full_FinancialInstrumentsDesignatedAsHedgingInstrumentsAtFairValue
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant