Derivatives (Narrative) (Details) gal in Millions, CAD in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) gal	Dec. 31, 2016 CAD gal	Dec. 31, 2015 USD ($) gal	Dec. 31, 2014 USD ($) gal
Diesel swap
Derivative [Line Items]
Derivative, nonmonetary notional amount (in gallons)	7.0	7.0
Forward contracts
Derivative [Line Items]
Derivative purchases of underlying currency (in Canadian Dollars) | CAD		CAD 894
Swap
Derivative [Line Items]
Hedging activities net cash flow impact | $	$ 29		$ 35	$ 41
Derivative purchases of underlying commodity (in gallons)	10.1	10.1	10.6	10.5