Marketable Securities and Restricted Funds Schedule of Restricted and Non-restricted Available for Sale Securities (Details) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		$ 37	$ 31
Investments and other assets—other
Schedule of Available-for-sale Securities [Line Items]
Restricted funds, Investments and other assets - other		31	11
Current assets—other
Schedule of Available-for-sale Securities [Line Items]
Non-restricted funds, Current assets - other		6	20
Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	[1]	20	31
Canadian Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	[2]	$ 17	$ 0

[1] Amounts related to certain construction projects.

[2] Amounts related to restricted funds held and collected from customers of Western Canada Transmission & Processing and Express-Platte for Canadian pipeline abandonment in accordance with the NEB’s regulatory requirements.