Income Taxes Schedule of Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Components of Deferred Tax Assets and Liabilities [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment	$ 1,531.0	$ 1,402.9
Deferred Tax Liabilities, Derivatives	60.4	127.7
Deferred Tax Liabilities, Net	1,591.4	1,530.6
Deferred Tax Assets Net Operating Loss And Tax Credit Carryforwards	51.9	11.7
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits	43.6	43.0
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Bonuses	7.0	16.3
Deferred Tax Assets, Other	9.1	12.4
Deferred Tax Assets, Gross	111.6	83.4
Deferred Tax Assets, Net of Valuation Allowance, Classification [Abstract]
Deferred Tax Assets, Net of Valuation Allowance, Current	0.0	0.0
Deferred income taxes	0.0	84.5
Deferred Tax Liabilities, Net, Noncurrent	1,479.8	1,362.7
Deferred Tax Liabilities, Net	$ 1,479.8	$ 1,447.2