Fair Value Measurements (Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets, Fair Value Disclosure [Abstract]
Assets from price risk management	$ 167.7	$ 173.1
SPH units	3.1	2.8
Assets, Fair Value Disclosure, Excluding Netting Adjustments	170.8	175.9
Netting Agreements	(122.3)	(140.3)
Derivative Asset, Fair Value of Collateral	(2.2)	1.9
Assets from price risk management, Total	43.2	34.7
Total assets at fair value	46.3	37.5
Liabilities, Fair Value Disclosure [Abstract]
Liabilities from price risk management	154.7	151.7
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	154.7	151.7
Netting Agreements	(122.3)	(140.3)
Derivative Liability, Fair Value of Collateral	(25.7)	(5.6)
Liabilities from price risk management, Total	6.7	5.8
Total liabilities at fair value		5.8
Level 1
Assets, Fair Value Disclosure [Abstract]
Assets from price risk management	3.7	12.4
SPH units	3.1	2.8
Assets, Fair Value Disclosure, Excluding Netting Adjustments	6.8	15.2
Liabilities, Fair Value Disclosure [Abstract]
Liabilities from price risk management	2.8	7.0
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	2.8	7.0
Level 2
Assets, Fair Value Disclosure [Abstract]
Assets from price risk management	164.0	160.7
SPH units	0.0	0.0
Assets, Fair Value Disclosure, Excluding Netting Adjustments	164.0	160.7
Liabilities, Fair Value Disclosure [Abstract]
Liabilities from price risk management	151.9	144.7
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	151.9	144.7
Level 3
Assets, Fair Value Disclosure [Abstract]
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, Fair Value Disclosure [Abstract]
Liabilities from price risk management	0.0	0.0
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	$ 0.0	$ 0.0