Fair Value Measurements (Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from price risk management	$ 290.3	$ 167.7
SPH units	2.0	3.1
Assets, Fair Value Disclosure, Excluding Netting Adjustments	292.3	170.8
Netting agreements	(235.0)	(122.3)
Derivative Asset, Fair Value of Collateral	(2.6)	(2.2)
Assets from price risk management, total	52.7	43.2
Total assets at fair value	54.7	46.3
Liabilities from price risk management	269.3	154.7
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	269.3	154.7
Netting agreements	(235.0)	(122.3)
Derivative Liability, Fair Value of Collateral	(28.7)	(25.7)
Liabilities from price risk management, total	5.6	6.7
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from price risk management	35.3	3.7
SPH units	2.0	3.1
Assets, Fair Value Disclosure, Excluding Netting Adjustments	37.3	6.8
Liabilities from price risk management	31.6	2.8
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	31.6	2.8
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from price risk management	255.0	164.0
SPH units	0.0	0.0
Assets, Fair Value Disclosure, Excluding Netting Adjustments	255.0	164.0
Liabilities from price risk management	237.7	151.9
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	237.7	151.9
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from price risk management	0.0	0.0
SPH units	0.0	0.0
Assets, Fair Value Disclosure, Excluding Netting Adjustments	0.0	0.0
Liabilities from price risk management	0.0	0.0
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	$ 0.0	$ 0.0