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Employee Benefit Plans (Change in AOCI ) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 CAD ($)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance, January 1	$ 636
Balance, December 31	563
Pension Plan [Member] | Defined Benefit Plans Adjustment, Net Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance, January 1	330
Amortized in current period, Net Actuarial Gain (Loss)	(38)
Current year addition to AOCI	(8)
Balance, December 31	284
Pension Plan [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance, January 1	(3)
Amortized in current period, Net Prior Service Cost (Credit)	0
Current year addition to AOCI	0
Balance, December 31	(3)
Pension Plan [Member] | Regulatory Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance, January 1	309
Amortized in current period, Net Actuarial Gain (Loss)	(17)
Current year addition to AOCI	(10)
Balance, December 31	282
Non-pension Benefit Plans [Member
Defined Benefit Plan Disclosure [Line Items]
Balance, January 1	44
Balance, December 31	74
Non-pension Benefit Plans [Member | Defined Benefit Plans Adjustment, Net Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance, January 1	15
Amortized in current period, Net Actuarial Gain (Loss)	(2)
Current year addition to AOCI	(2)
Balance, December 31	11
Non-pension Benefit Plans [Member | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance, January 1	(19)
Amortized in current period, Net Prior Service Cost (Credit)	8
Current year addition to AOCI	0
Balance, December 31	(11)
Non-pension Benefit Plans [Member | Regulatory Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance, January 1	48
Amortized in current period, Net Actuarial Gain (Loss)	1
Current year addition to AOCI	25
Balance, December 31	$ 74

X

- Definition

Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (i-k)
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580

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- Definition

Amount, before tax, after reclassification adjustment, of increase (decrease) in accumulated other comprehensive income from gain (loss) of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 220
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-Paragraph 10A
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-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580

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-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 220
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-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

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