Supplemental Information (Supplementary Cash Flow Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplementary Information [Abstract]
Interest Paid	$ 370	$ 397	$ 602
Income Taxes Paid, net of Amounts Recovered	$ (77)	$ (19)	$ (105)