Asset Impairments (Narrative) (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Impaired Long-Lived Assets Held and Used [Line Items]
Goodwill	$ 3,964,000,000	$ 5,032,000,000	$ 6,303,000,000
Canada [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Goodwill			$ 0