Properties, Plant and Equipment - Other Property, Plant and Equipment - Depreciation and Amortization (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other Property, Plant and Equipment
Depreciation and amortization of other property, plant and equipment	$ 0.2	$ 0.3	$ 0.5	$ 0.6