Fair Value Measurements (Narrative) (Details) gal in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) $ / gal gal	Dec. 31, 2014 USD ($)
Level 3 | National Pump | Accrued expenses and other liabilities
Derivatives, Fair Value [Line Items]
Contingent consideration | $	$ 0	$ 78
Merger related costs
Derivatives, Fair Value [Line Items]
Change in contingent consideration | $	$ (26)
Diesel swap | Swap
Derivatives, Fair Value [Line Items]
Derivative, nonmonetary notional amount (in gallons) | gal	10.3
Derivative, notional amount (in dollars per gallon) | $ / gal	2.93
Average forward price (in dollars per gallon) | $ / gal	2.35