financial instruments - Activity related to allowance for doubtful accounts (Details) - Customer accounts receivable - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Summary of activity related to allowance for doubtful accounts
Balance, beginning of period	$ (1,257)
Balance, end of period	(1,749)	$ (1,257)
Allowance for doubtful accounts
Summary of activity related to allowance for doubtful accounts
Balance, beginning of period	53	43
Additions (doubtful accounts expense)	64	56
Accounts written off, net of recoveries	(66)	(55)
Other	4	9
Balance, end of period	$ 55	$ 53

- Definition

The amount of assets that are: (a) cash; (b) an equity instrument of another entity; (c) a contractual right: (i) to receive cash or another financial asset from another entity; or (ii) to exchange financial assets or financial liabilities with another entity under conditions that are potentially favourable to the entity; or (d) a contract that will, or may be, settled in the entity’s own equity instruments and is: (i) a non-derivative for which the entity is, or may be, obliged to receive a variable number of the entity’s own equity instruments; or (ii) a derivative that will, or may be, settled other than by the exchange of a fixed amount of cash or another financial asset for a fixed number of the entity’s own equity instruments. For this purpose the entity’s own equity instruments do not include puttable financial instruments classified as equity instruments in accordance with paragraphs 16A-16B of IAS 32, instruments that impose on the entity an obligation to deliver to another party a pro rata share of the net assets of the entity only on liquidation and are classified as equity instruments in accordance with paragraphs 16C-16D of IAS 32, or instruments that are contracts for the future receipt or delivery of the entity’s own equity instruments. [Refer: Financial instruments, class [member]; Financial liabilities]

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