Employee Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Contribution to defined benefit pension plan			$ 0
Defined benefit plan, estimated future employer contributions in current fiscal year	3.0		3.0
Defined Contribution Plan, Cost Recognized	2.2	2.0	4.4	4.1
Retirement Plans [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	1.1	1.0	2.2	2.0
Interest cost	1.2	1.5	2.4	2.9
Expected return on plan assets	(2.3)	(2.2)	(4.5)	(4.3)
Amortization of prior service credit	0	0	0	0
Amortization of unrecognized net loss	0.6	0.5	1.2	1.0
Net periodic benefit cost	0.6	0.8	1.3	1.6
PBOP [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0.1	0.1	0.2	0.2
Interest cost	0.4	0.6	0.9	1.2
Expected return on plan assets	(1.1)	(1.0)	(2.2)	(2.1)
Amortization of prior service credit	(1.9)	(2.0)	(3.8)	(3.9)
Amortization of unrecognized net loss	(0.1)	0	0	0.1
Net periodic benefit cost	$ (2.6)	$ (2.3)	$ (4.9)	$ (4.5)