Consolidated statement of comprehensive income (U.S. GAAP, unaudited) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 1,195	$ 1,248
Other comprehensive income (loss), net of income taxes
Postretirement benefits liability adjustment (excluding amortization)	4	21
Amortization of postretirement benefits liability adjustment included in net benefit costs	12	10
Total other comprehensive income (loss)	16	31
Comprehensive income (loss)	$ 1,211	$ 1,279