Components of Net Periodic Benefit Cost and Changes in Amounts Recorded in Accumulated Other Comprehensive Income (Detail) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Total recorded in other comprehensive income	CAD (316)	CAD 456	CAD (990)
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Current service cost	211	152	181
Interest cost	307	322	281
Expected return on plan assets	(392)	(369)	(331)
Amortization of prior service cost	16	23	23
Amortization of actuarial loss/(gain)	198	166	243
Net periodic benefit cost	340	294	397
Net actuarial loss/(gain)	(86)	529	(664)
Amortization of net actuarial (loss)/gain included in net periodic benefit cost	(198)	(166)	(243)
Amortization of prior service cost included in net periodic benefit cost	(16)	(23)	(23)
Total recorded in other comprehensive income	(300)	340	(930)
Total recorded in net periodic benefit cost and other comprehensive income, before tax	40	634	(533)
Other post-retirement benefits
Defined Benefit Plan Disclosure [Line Items]
Current service cost	15	9	11
Interest cost	25	26	21
Amortization of actuarial loss/(gain)	14	7	10
Net periodic benefit cost	54	42	42
Net actuarial loss/(gain)	(2)	123	(50)
Amortization of net actuarial (loss)/gain included in net periodic benefit cost	(14)	(7)	(10)
Total recorded in other comprehensive income	(16)	116	(60)
Total recorded in net periodic benefit cost and other comprehensive income, before tax	CAD 38	CAD 158	CAD (18)