Commitments and Contingencies (Lawsuits) (Details) - Emergency Pricing And Consumer Protection Laws - Pending Litigation $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Plaintiff	Commonwealth of Kentucky
Alleged amount overcharged from customers	$ 89
Loss contingency, period of occurrence	during September and October 2005