Derivatives, Hedging Programs and Other Financial Instruments, Offsetting of Derivative Instruments by Counterparty (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Gross Amounts of Recognized Assets	$ 10.4	$ 5.8
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	10.4	5.8
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	2.8	1.7
Net Amount	7.6	4.1
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract]
Gross Amounts of Recognized Liabilities	(2.8)	(1.8)
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(2.8)	(1.8)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	(2.8)	(1.7)
Net Amount	0.0	(0.1)
Counterparty (with Netting Agreements)
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Gross Amounts of Recognized Assets	10.4	3.3
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	10.4	3.3
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	2.8	1.0
Net Amount	7.6	2.3
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract]
Gross Amounts of Recognized Liabilities	(2.8)	(1.0)
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(2.8)	(1.0)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	(2.8)	(1.0)
Net Amount	$ 0.0	0.0
Counterparty (with partial Netting Agreements)
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Gross Amounts of Recognized Assets		2.5
Gross Amounts Offset in the Consolidated Balance Sheets		0.0
Net Amounts of Assets Presented in the Consolidated Balance Sheets		2.5
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments		0.7
Net Amount		1.8
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract]
Gross Amounts of Recognized Liabilities		(0.8)
Gross Amounts Offset in the Consolidated Balance Sheets		0.0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets		(0.8)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments		(0.7)
Net Amount		$ (0.1)