Consolidated statement of shareholders' equity (U.S GAAP, unaudited) - CAD ($) $ in Millions	Total	Common shares at stated value (note 9)	Earnings reinvested	Accumulated other comprehensive income (loss) (note 10)
At beginning of period at Dec. 31, 2022		$ 1,079	$ 21,846	$ (512)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share purchases at stated value		0
Net income (loss) for the period	$ 1,248		1,248
Share purchases in excess of stated value			0
Dividends declared			(257)
Other comprehensive income (loss)	31			31
At end of period at Mar. 31, 2023	23,435	1,079	22,837	(481)
At beginning of period at Dec. 31, 2022		1,079	21,846	(512)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share purchases at stated value		(87)
At end of period at Dec. 31, 2023	22,222	992	21,907	(677)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share purchases at stated value		0
Net income (loss) for the period	1,195		1,195
Share purchases in excess of stated value			0
Dividends declared			(321)
Other comprehensive income (loss)	16			16
At end of period at Mar. 31, 2024	$ 23,112	$ 992	$ 22,781	$ (661)