Acquisition Purchase Price Allocation (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Jun. 29, 2015
Business Combinations [Abstract]
Duration of the measurement period	1 year
Assets acquired
Current assets				$ 1,069.9
Net property, plant, and equipment				7,091.8
Investments				1,062.5
Goodwill	$ 2,581.6	$ 2,581.6	$ 0.0
Deferred charges and other assets, excluding goodwill				1,737.9
Liabilities assumed
Current liabilities, including current maturities of long-term debt				(1,293.5)
Deferred credits and other liabilities				(3,668.5)
Long-term debt				(2,947.5)
Preferred stock of subsidiary				$ (51.1)
Total purchase price	$ 5,583.1