Derivatives (Cash Flow Hedges in AOCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedge derivative gains (losses) expected to be reclassified into earnings within the next 12 months	$ 8.2
Commodity Price Hedges [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized losses on unsettled contracts	13.2	$ 7.2
Income tax expense (benefit)	(4.8)	(2.6)
Losses included in AOCI, net of tax	$ 8.4	$ 4.6