Pension and Postretirement Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Capitalized portion of defined benefit contribution percent	10.00%	10.00%
Defined Benefit Plan, Expected Contributions in Current Fiscal Year			$ 25
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Contributions	2.6
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	0	0.3
Interest cost on projected benefit obligation	4.6	4.5
Expected return on plan assets	(7.2)	(6.8)
Amortization of:
Prior service cost (benefit)	0.1	0
Actuarial loss	5.1	5.3
Total amortization	5.2	5.3
Benefit costs (benefits)	2.6	3.3
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Contributions	2.0
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	0.1	0.1
Interest cost on projected benefit obligation	0.8	0.9
Expected return on plan assets	0	0
Amortization of:
Prior service cost (benefit)	(3.9)	(3.8)
Actuarial loss	1.4	1.3
Total amortization	(2.5)	(2.5)
Benefit costs (benefits)	(1.6)	(1.5)