Pensions and Other Postretirement Benefits (Rollforward of Fair Value of Investments Classified as Level 3) (Details) - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 18,564
Fair value of plan assets at end of year	17,244	$ 18,564
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	410
Fair value of plan assets at end of year	421	410
Oil and Gas [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	1,120
Fair value of plan assets at end of year	948	1,120
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	1,101	1,046
Actual return relating to assets still held at the reporting date	(13)	107
Purchases	1
Sales	(1)
Disbursements	(39)	(52)
Fair value of plan assets at end of year	1,049	1,101
Fair Value, Inputs, Level 3 [Member] \| Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	332	324
Actual return relating to assets still held at the reporting date	(2)	19
Purchases	1
Sales	(1)
Disbursements	(9)	(11)
Fair value of plan assets at end of year	321	332
Fair Value, Inputs, Level 3 [Member] \| Oil and Gas [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	769	722
Actual return relating to assets still held at the reporting date	(11)	88
Purchases	0
Sales	0
Disbursements	(30)	(41)
Fair value of plan assets at end of year	$ 728	$ 769

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+ References

No definition available.

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References

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+ References

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+ References

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