Business, Basis of Presentation and Significant Accounting Policies (Remaining Performance Obligations) (Narrative) (Details) $ in Billions	3 Months Ended
	Mar. 31, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue recognition, remaining performance obligations, contract price allocated (in dollars)	$ 3.9
Revenue recognition, remaining performance obligations, completion period (in months/years)	9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue recognition, remaining performance obligations, contract price allocated (in dollars)	$ 5.4
Revenue recognition, remaining performance obligations, completion period (in months/years)