Pension and Other Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Mar. 31, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan contributions				$ 170.0	$ 110.0
Net periodic benefit cost (income) [Abstract]
Expected plan contributions during the year	170.0			170.0
Noncash reduction in the value of deferred tax asset resulting from a change in Medicare Part D reimbursement tax treatment	0	0		2.0	25.3
Amortization period on remaining portion of reversed prior amortization recorded in other comprehensive income (in years)	5			5
Middletown Retirees [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Net periodic benefit cost (income) [Abstract]
Contributions to Middletown retirees VEBA				65.0
Pension Plans, Defined Benefit [Member]
Net periodic benefit cost (income) [Abstract]
Service cost	0.8	0.8		2.4	2.5
Interest cost	45.1	47.9		135.5	143.7
Expected return on assets	(51.7)	(48.9)		(155.6)	(146.8)
Amortization of prior service cost credit	1.2	0.9		3.2	2.5
Amortization of (gain) loss	4.7	4.4		14.1	13.0
Net periodic benefit cost (income)	0.1	5.1		(0.4)	14.9
Other Postretirement Benefit Plans, Defined Benefit [Member]
Net periodic benefit cost (income) [Abstract]
Service cost	1.1	1.0		3.2	3.1
Interest cost	9.4	10.8		28.6	32.3
Settlement gain related to Middletown Retiree Settlement	0	0		(14.0)	0
Amortization of prior service cost credit	(19.2)	(19.8)		(57.5)	(59.2)
Reversal of prior amortization related to Butler Retiree Settlement	0	0		14.2	0
Amortization of (gain) loss	(0.3)	(0.6)		(0.8)	(1.9)
Net periodic benefit cost (income)	(9.0)	(8.6)		(26.3)	(25.7)
Increase in OPEB liability due to effect settlement				29.6
Decrease in amortization of gain for Other Postretirement Benefits as a result of a preliminary injunction		0.4			1.2
Net increase in liability due to remeasurement of OPEB liability				4.3
Discount rate used to measure OPEB liability	5.18%			5.18%		5.26%
Noncash reduction in the value of deferred tax asset resulting from a change in Medicare Part D reimbursement tax treatment			$ 25.3