Fair Value Measurements (Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from price risk management	$ 554.7	$ 728.9
Other investments	2.3	2.2
Assets, Fair Value Disclosure, Excluding Netting Adjustments	557.0	731.1
Netting agreements	(474.5)	(607.4)
Assets, Collateral/Margin Received or Paid	(46.0)	(79.4)
Assets from price risk management, total	34.2	42.1
Total assets at fair value	36.5	44.3
Liabilities from price risk management	560.0	713.2
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	560.0	713.2
Netting agreements	(474.5)	(607.4)
Liabilities, Collateral/Margin Received or Paid	(3.2)	(8.8)
Liabilities from price risk management, total	82.3	114.6
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from price risk management	42.5	33.3
Other investments	2.3	2.2
Assets, Fair Value Disclosure, Excluding Netting Adjustments	44.8	35.5
Liabilities from price risk management	55.6	26.9
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	55.6	26.9
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from price risk management	512.2	695.6
Other investments	0.0	0.0
Assets, Fair Value Disclosure, Excluding Netting Adjustments	512.2	695.6
Liabilities from price risk management	504.4	686.3
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	504.4	686.3
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from price risk management	0.0	0.0
Other investments	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