Components of Net Periodic Benefit Cost and Changes in Amounts Recorded in Accumulated Other Comprehensive Income (Detail) (CAD) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Total recorded in other comprehensive income	456	(990)	304
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Current service cost	152	181	160
Interest cost	322	281	288
Expected return on plan assets	(369)	(331)	(288)
Amortization of prior service cost	23	23	23
Amortization of actuarial loss/(gain)	166	243	235
Net periodic benefit cost	294	397	418
Net actuarial loss/(gain)	529	(664)	530
Amortization of net actuarial (loss)/gain included in net periodic benefit cost	(166)	(243)	(235)
Amortization of prior service cost included in net periodic benefit cost	(23)	(23)	(23)
Total recorded in other comprehensive income	340	(930)	272
Total recorded in net periodic benefit cost and other comprehensive income, before tax	634	(533)	690
Other post-retirement benefits
Defined Benefit Plan Disclosure [Line Items]
Current service cost	9	11	8
Interest cost	26	21	21
Amortization of actuarial loss/(gain)	7	10	8
Net periodic benefit cost	42	42	37
Net actuarial loss/(gain)	123	(50)	40
Amortization of net actuarial (loss)/gain included in net periodic benefit cost	(7)	(10)	(8)
Total recorded in other comprehensive income	116	(60)	32
Total recorded in net periodic benefit cost and other comprehensive income, before tax	158	(18)	69

Amount recognized in net periodic benefit cost and other comprehensive income.

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The amount of gains or losses recognized in net periodic benefit cost.

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The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

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An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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Amount before tax of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) related to pension and other postretirement benefit plans.

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Amount before tax, after reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.

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Amount before tax of (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit.

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Amount before tax of reclassification adjustment from accumulated other comprehensive income (loss) for actuarial gain (loss) related to pension and other postretirement benefit plans.

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