Employee Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 employee fund	Dec. 31, 2013	Dec. 31, 2012
Number of Fixed Income Funds Investing in Debt Securities Ecured by Royalty Payments [Line Items]
Number of Private Equity Funds Investing in Renewable Solar Energy	5
Number of employees sponsored by defined benefit pension plans	12,000
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 1,188.8	$ 1,345.7
Service cost	4.3	4.3	3.9
Interest cost	60.7	56.2	59.3
Benefits paid	(101.1)	(76.5)
Actuarial loss	214.1	(131.6)
Expenses paid from assets	(11.3)	(9.6)
Other	(0.3)	0.3
Benefit obligation at year end	1,355.2	1,188.8	1,345.7
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at prior year end	808.4	799.4
Actual return on plan assets	141.6	31.9
Employer contributions	62.3	62.9
Benefits paid	(101.1)	(76.5)
Expenses paid from assets	(11.3)	(9.6)
Other	(0.6)	0.3
Fair value of plan assets at year end	899.3	808.4	799.4
Funded status at year end	(455.9)	(380.4)
Noncurrent assets	1.9	1.7
Current liabilities	0.4	0.6
Noncurrent liabilities	457.4	381.5
Net actuarial loss	502.7	389.2
Unrecognized actuarial losses net of tax	448.6
Actuarial loss included in accumulated other comprehensive income and expected to be recognized next year	$ 16.4
Fixed Income Funds [Member]
Number of Fixed Income Funds Investing in Debt Securities Ecured by Royalty Payments [Line Items]
Number of Fixed Income Funds Investing in Debt Securities Secured by Royalty Payments		3