Derivatives (Narrative) (Details) gal in Millions, CAD in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) gal	Dec. 31, 2015 CAD gal	Dec. 31, 2014 USD ($) gal	Dec. 31, 2013 USD ($) gal
Swap
Derivative [Line Items]
Hedging activities net cash flow impact | $	$ 35		$ 41	$ 38
Derivative purchases of underlying commodity (in gallons)	10.6	10.6	10.5	9.7
Foreign contracts
Derivative [Line Items]
Derivative purchases of underlying currency (in Canadian Dollars) | CAD		CAD 221
Diesel swap | Swap
Derivative [Line Items]
Derivative, nonmonetary notional amount (in gallons)	10.3	10.3