Postretirement Benefits Other Than Pensions - Changes in Fair Value of Plan Assets and Changes in Accumulated Benefit Obligations (Details) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	$ 0	$ 0
Employer Contributions	3.0	3.2
Plan Participants' Contributions	1.0	1.1
Benefits Paid	(4.0)	(4.3)
Fair Value of Plan Assets at End of Year	0	0	0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligations at Beginning of Year	44.7	41.1
Service Cost	0.2	0.1	0.1
Interest Cost	1.6	1.9	2.1
Plan Participants' Contributions	1.0	1.1
Benefits Paid	(4.0)	(4.3)
Modernization Act Subsidy Received	1.0	0.4
Actuarial Losses	(5.5)	4.4
Obligations Transferred Into Plan	3.8	0
Benefit Obligations at End Of Year	42.8	44.7	41.1
Funded Status - Benefit Obligation In Excess of Plan Assets	(42.8)	(44.7)
Actuarial Gain Recognized in Accumulated Other Comprehensive Income	$ 13.4	$ 9.2