Risk Management And Energy Marketing Activities (The Effect Of Derivative Instruments Reclassified To Statements Of Consolidated Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Fair Value Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain Recognized in Income on Derivatives	$ (8.3)		$ (3.0)		$ (16.5)		$ (3.5)
Amount of Gain Recognized in Income on Related Hedged Items	8.3		3.0		16.5		3.5
Cash Flow Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain Recognized in OCI Derivative (Effective Portion)	0.6		0.2		2.0		1.5
Amount of Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	(0.7)		(0.6)		(2.8)		(1.1)
Amount of Gain Recognized in Income on Derivatives	0		0		0		0
Not Designated As Hedging Instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain Recognized in Income on Derivatives	7.4	[1]	9.1	[1]	(5.5)	[2]	(2.1)	[2]
Cost Of Sales [Member] | Cash Flow Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	0		0.1		(0.8)		0.9
Interest Expense [Member] | Cash Flow Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	(0.7)		(0.7)		(2.0)		(2.0)
Commodity Price Risk Programs [Member] | Cash Flow Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain Recognized in OCI Derivative (Effective Portion)	0.2		(0.2)		0.8		0.3
Commodity Price Risk Programs [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Losses recognized in income, deferred	6.8		9.4		(8.3)		(9.8)
Commodity Price Risk Programs [Member] | Gas Distribution Revenues [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain Recognized in Income on Derivatives	0	[1]	(0.1)	[1]	0.3	[2]	(21.8)	[2]
Commodity Price Risk Programs [Member] | Cost Of Sales [Member] | Cash Flow Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain Recognized in Income on Derivatives	0		0		0		0
Commodity Price Risk Programs [Member] | Cost Of Sales [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain Recognized in Income on Derivatives	2.4	[1]	(7.4)	[1]	(16.8)	[2]	(15.3)	[2]
Commodity Price Risk Programs [Member] | Other Revenues [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain Recognized in Income on Derivatives	5.0	[1]	16.6	[1]	11.0	[2]	35.0	[2]
Interest Rate Risk Activities [Member] | Cash Flow Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain Recognized in OCI Derivative (Effective Portion)	0.4		0.4		1.2		1.2
Interest Rate Risk Activities [Member] | Interest Expense [Member] | Fair Value Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain Recognized in Income on Derivatives	(8.3)		(3.0)		(16.5)		(3.5)
Interest Rate Risk Activities [Member] | Interest Expense [Member] | Cash Flow Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain Recognized in Income on Derivatives	0		0		0		0
Fixed Rate Debt Hedges [Member] | Interest Expense [Member] | Fair Value Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain Recognized in Income on Related Hedged Items	$ 8.3		$ 3.0		$ 16.5		$ 3.5

[1] * For the amounts of realized/unrealized gain (loss) recognized in income on derivatives disclosed in the table above, gains of $6.8 million and $9.4 million for the three months ended September 30, 2012 and 2011, respectively, were deferred as allowed by regulatory orders. These amounts will be amortized to income over future periods of up to twelve months as specified in a regulatory order.

[2] * For the amounts of realized/unrealized gain (loss) recognized in income on derivatives disclosed in the table above, losses of $8.3 million and $9.8 million for the nine months ended September 30, 2012 and 2011, respectively, were deferred as allowed per regulatory orders. These amounts will be amortized to income over future periods of up to twelve months as specified in a regulatory order.