Income Taxes - Income Tax Adjustments, Settlements and Unusual Items (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Settlements, Adjustments and Unusual Items [Line Items]
Income Tax Adjustments, Settlements and Unusual Items	$ (13)
Valuation Allowance, Deferred Tax Asset, Change in Amount	9
CANADA
Income Tax Settlements, Adjustments and Unusual Items [Line Items]
Income Tax Adjustments, Settlements and Unusual Items	(10)
Pension Plan [Member]
Income Tax Settlements, Adjustments and Unusual Items [Line Items]
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements	$ 0	$ (427)	$ 1