Employee Benefits (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 29, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Contribution to defined benefit pension plan	$ 7.5
Defined Contribution Plan, Cost Recognized		1.9	2.0	6.0	5.8
Retirement Plans [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Service Cost		1.0	1.0	3.0	3.0
Defined Benefit Plan, Interest Cost		1.4	1.6	4.3	4.8
Expected return on plan assets		(2.1)	(2.0)	(6.4)	(6.0)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		0	0	0	0
Amortization of unrecognized net loss		0.5	0.3	1.5	0.9
Regulatory asset (increase) decrease		0	0	0	0
Net periodic benefit cost		0.8	0.9	2.4	2.7
PBOP [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Service Cost		0.1	0.1	0.3	0.3
Defined Benefit Plan, Interest Cost		0.6	0.6	1.8	1.8
Expected return on plan assets		(1.1)	(0.8)	(3.2)	(2.4)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		(1.9)	(1.9)	(5.8)	(5.7)
Amortization of unrecognized net loss		0	0.1	0.1	0.4
Regulatory asset (increase) decrease		0	1.4	0	4.2
Net periodic benefit cost		$ (2.3)	$ (0.5)	$ (6.8)	$ (1.4)