Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill, Beginning Balance	$ 2,779
Goodwill, Ending Balance	2,609	$ 2,779
United States [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	2,129	2,129
Divested During the Year	(216)	0
Goodwill, Ending Balance	1,913	2,129
Canada [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	650	661
Divested During the Year		(32)
Foreign Currency Translation Adjustment	46	21
Goodwill, Ending Balance	$ 696	$ 650