Fair Value Measurements (Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from price risk management	$ 1,543.2	$ 500.7
SPH units	2.2	2.1
Assets, Fair Value Disclosure, Excluding Netting Adjustments	1,545.4	502.8
Netting agreements	(1,339.6)	(455.0)
Assets, Collateral/Margin Received or Paid	(164.5)	(18.5)
Assets from price risk management, total	39.1	27.2
Total assets at fair value	41.3	29.3
Liabilities from price risk management	1,603.2	519.1
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	1,603.2	519.1
Netting agreements	(1,339.6)	(455.0)
Liabilities, Collateral/Margin Received or Paid	13.7	12.2
Liabilities from price risk management, total	277.3	76.3
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from price risk management	74.2	20.2
SPH units	2.2	2.1
Assets, Fair Value Disclosure, Excluding Netting Adjustments	76.4	22.3
Liabilities from price risk management	55.8	25.1
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	55.8	25.1
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from price risk management	1,469.0	480.5
SPH units	0.0	0.0
Assets, Fair Value Disclosure, Excluding Netting Adjustments	1,469.0	480.5
Liabilities from price risk management	1,547.4	494.0
Liabilities, Fair Value Disclosure, Excluding Netting Adjustments	1,547.4	494.0
Fair Value, Inputs, Level 3 [Member]
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