Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Plans [Member]
Change in Benefit Obligation
Benefit Obligation at January 1	$ 1,508.5	$ 1,330.6
Service cost	14.6	21.7	15.9
Interest cost	60.4	65.5	67.6
Participants' contributions	0	0
Plan amendments	(1.0)	0
Actuarial loss (gain)	(81.9)	166.5
Curtailments	0	31.4
Gross benefits paid	(90.4)	(107.2)
Benefit Obligation at December 31	1,410.2	1,508.5	1,330.6
OPEB [Member]
Change in Benefit Obligation
Benefit Obligation at January 1	381.2	389.7
Service cost	10.0	10.3	10.4
Interest cost	15.6	20.3	20.8
Participants' contributions	8.9	9.6
Plan amendments	0	0.5
Actuarial loss (gain)	(27.7)	(23.8)
Curtailments	0	0
Gross benefits paid	(26.3)	(26.3)
Federal subsidy on benefits paid	1.0	0.9
Benefit Obligation at December 31	$ 362.7	$ 381.2	$ 389.7