Derivatives (Cash Flow Hedges in AOCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedge derivative gains (losses) expected to be reclassified into earnings within the next 12 months	$ 4.5
Commodity Price Hedges [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized (gains) losses on unsettled contracts	(8.9)	$ 13.2
Income tax expense (benefit)	3.3	(4.8)
Losses included in AOCI, net of tax	$ (5.6)	$ 8.4