Regulatory Matters - Regulatory Liabilities (Details) - USD ($) $ in Millions		1 Months Ended			12 Months Ended
		Jul. 31, 2016	Oct. 31, 2015	Nov. 30, 2014	Dec. 31, 2016	Dec. 31, 2015
Regulatory Liabilities [Line Items]
Regulatory liabilities					$ 187	$ 402
Regulatory liabilities, noncurrent					2,933	2,631
Regulatory Liabilities					3,120	3,033
Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[1]				$ 2,242	2,167
Weighted average remaining life	[1]				27 years
Deferred net power costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities					$ 64	206
Weighted average remaining life					1 years
Asset Retirement Obligation Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities					$ 122	147
Weighted average remaining life					35 years
Levelized depreciation [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities					$ 244	199
Weighted average remaining life					23 years
Impact fees [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities					$ 90	0
Weighted average remaining life					6 years
Employee benefit plans [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[2]				$ 25	13
Weighted average remaining life	[2]				12 years
Unrealized gain on regulated derivative contracts [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[2]				$ 6	0
Weighted average remaining life	[2]				1 year
Regulatory liabilities other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities					$ 327	$ 301
Weighted average remaining life					Various
Amount for discontinuance of CWIP in rate base [Member] | Alberta Utilities Commission [Member]
Regulatory Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount			$ 82
Amount for change to flow through method for income taxes [Member] | Alberta Utilities Commission [Member]
Regulatory Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 45
AltaLink [Member] | Alberta Utilities Commission [Member]
Regulatory Liabilities [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 415
Public Utilities, Approved Rate Increase (Decrease), Amount					200
AltaLink [Member] | 2015-2016 GTA [Member] | GTA 2015 [Member] | Alberta Utilities Commission [Member]
Regulatory Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		599
AltaLink [Member] | 2015-2016 GTA [Member] | GTA 2016 [Member] | Alberta Utilities Commission [Member]
Regulatory Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		685
AltaLink [Member] | Amount previously collected as CWIP given as refund [Member] | Alberta Utilities Commission [Member]
Regulatory Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		277			$ 200
AltaLink [Member] | Amount previously collected as CWIP given as returns [Member] | Alberta Utilities Commission [Member]
Regulatory Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		12
AltaLink [Member] | Amount for change to flow through method for income taxes [Member] | Alberta Utilities Commission [Member]
Regulatory Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 68
2015-2016 GTA [Member] | AltaLink [Member] | GTA 2015 [Member] | Alberta Utilities Commission [Member]
Regulatory Liabilities [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			672	$ 811
2015-2016 GTA [Member] | AltaLink [Member] | GTA 2016 [Member] | Alberta Utilities Commission [Member]
Regulatory Liabilities [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 704	$ 1,000

[1] Amounts represent estimated costs, as accrued through depreciation rates and exclusive of ARO liabilities, of removing regulated property, plant and equipment in accordance with accepted regulatory practices. Amounts are deducted from rate base or otherwise accrue a carrying cost.

[2] Represents amounts not yet recognized as a component of net periodic benefit cost that are to be returned to customers in future periods when recognized.ALP General Tariff Application ("GTA")In November 2014, ALP filed a GTA requesting the Alberta Utilities Commission ("AUC") to approve revenue requirements of C$811 million for 2015 and C$1.0 billion for 2016, primarily due to continued investment in capital projects as directed by the Alberta Electric System Operator. ALP amended the GTA in June 2015 to propose transmission tariff relief measures for customers and modifications to its capital structure. ALP also amended and updated the GTA in October 2015, reducing the requested revenue requirements to C$672 million for 2015 and C$704 million for 2016. In May 2016, the AUC issued its decision pertaining to the 2015-2016 GTA. ALP filed its 2015-2016 GTA compliance filing in July 2016 to comply with the AUC's decision.The compliance filing requested the AUC to approve revenue requirements of C$599 million for 2015 and C$685 million for 2016. The decreased revenue requirements requested in the compliance filing, as compared to the 2015-2016 GTA filing updated in October 2015, were primarily due to the AUC approval of ALP's proposed immediate tariff relief of C$415 million for customers for 2015 and 2016, through (i) the discontinuance of construction work-in-progress ("CWIP") in rate base and the return to allowance for funds used during construction ("AFUDC") accounting effective January 1, 2015, resulting in a C$82 million reduction of revenue requirement and the refund of C$277 million previously collected as CWIP in rate base as part of ALP's transmission tariffs during 2011-2014 less related returns of C$12 million and (ii) a change to the flow through method for calculating income taxes for 2016, resulting in further tariff relief of C$68 million.Operating revenue for the year ended December 31, 2016, included a one-time reduction of $200 million from the 2015-2016 GTA decision received in May 2016 at ALP. The 2015-2016 GTA decision required ALP to refund $200 million to customers in 2016 through reduced monthly billings for the change from receiving cash during construction for the return on CWIP in rate base to recording allowance for borrowed and equity funds used during construction related to construction expenditures during the 2011 to 2014 time period. This amount is offset with higher capitalized interest and allowance for equity funds in the Consolidated Statements of Operations. In addition, the decision required ALP to change to the flow through method of recognizing income tax expense effective January 1, 2016. This change reduced operating revenue by $45 million for the year ended December 31, 2016, with offsetting impacts to income tax expense in the Consolidated Statements of Operations.