Commitments and Contingencies Commitments and Contingencies, Environmental Contingencies - Unrecorded Unconditional Purchase Obligation (Details) $ in Millions	Dec. 31, 2015 USD ($)	Oct. 30, 2015 Period
National Ambient Air Quality Standards for Ozone
Environmental Requirements [Abstract]
Number of hours measured for standard | Period		8
Current level of air quality concentrations (in parts per billion)		75
Proposed level of air quality concentrations (in parts per billion)		70
Capital Commitments | Federal Clean Water Act Section 316(b)
Environmental Requirements [Abstract]
Liability for estimated cost to comply with entrainment regulation | $	$ 4