Revenue Recognition (Narrative) (Details) $ in Billions	9 Months Ended
	Sep. 30, 2018 USD ($)
Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Payment term	30 days
Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Payment term	60 days
Up front customer loyalty programs and volume commitment programs
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimation of future revenues	$ 1.1