Employee Benefits (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Benefits
Balances in Deferred Compensation Plan	$ 13.5	$ 11.7
Value of assets for funding future payouts under the deferred compensation plan	12.9us-gaap_DeferredCompensationPlanAssets
Change in benefit obligation
Benefit obligation at end of year	9.9
Change in plan assets
Fair value of plan assets at end of year	72.4	70.2
Amounts recognized in the statement of financial position
Noncurrent liabilities	(102.2)	(84.0)
Supplemental Executive Retirement Plans
Change in benefit obligation
Benefit obligation at beginning of year	38.7	40.7
Service cost	0.9	0.9	0.9
Interest cost	1.5	1.5
Actuarial (gain) loss	6.1	(3.1)
Benefits paid	(1.3)	(1.3)
Benefit obligation at end of year	45.9	38.7	40.7
Funded status
Funded status of the plans	(45.9)	(38.7)
Items not yet recognized as component of net periodic pension expense
Unrecognized net actuarial losses	14.3	8.8
Unamortized prior service (credit) cost	(0.3)	(0.7)
Accumulated other comprehensive (income) loss	14.0	8.1
Amounts recognized in the statement of financial position
Current liabilities	(4.0)	(3.6)
Noncurrent liabilities	(41.9)	(35.1)
Accumulated other comprehensive (income) loss	14.0	8.1
Net amount recognized	(31.9)	(30.6)
Accumulated benefit obligation	44.6	38.7
Components of net periodic benefit cost
Service cost	0.9	0.9	0.9
Interest cost	1.5	1.5	1.5
Prior service (credit) cost	(0.5)	(0.5)	(0.5)
Amortization of net loss	0.7	1.3	1.0
Net periodic benefit cost	2.6	3.2	2.9
Weighted average assumptions to determine net cost
Discount rate (as a percent)	4.07%	3.73%	4.22%
Rate of compensation increase (as a percent)	6.00%	6.00%	6.00%
Weighted average assumptions to determine benefit obligations
Discount rate (as a percent)	2.94%	4.05%
Rate of compensation increase (as a percent)	6.00%	6.00%
Expected employer contributions during 2015	4.1
Defined Benefit Plans
Change in benefit obligation
Benefit obligation at beginning of year	82.0	85.0
Service cost	1.3	1.4	1.2
Interest cost	3.8	3.4
Actuarial (gain) loss	17.5	(8.7)
Benefits paid	(4.5)	(2.9)
Assumed in acquisition		3.5
Plan amendments	0.4	0.3
Benefit obligation at end of year	100.5	82.0	85.0
Change in plan assets
Fair value of plan assets at beginning of year	70.2	58.9
Acquired in acquisition		2.5
Actual return on plan assets	3.3	9.7
Employer contributions	3.3	2.0
Benefits paid	(4.4)	(2.9)
Fair value of plan assets at end of year	72.4	70.2	58.9
Funded status
Funded status of the plans	(28.1)	(11.8)
Items not yet recognized as component of net periodic pension expense
Unrecognized net actuarial losses	29.5	10.5
Unamortized prior service (credit) cost	1.7	1.5
Accumulated other comprehensive (income) loss	31.2	12.0
Amounts recognized in the statement of financial position
Noncurrent liabilities	(28.1)	(11.8)
Accumulated other comprehensive (income) loss	31.2	12.0
Net amount recognized	3.1	0.2
Accumulated benefit obligation	100.5	80.6
Information for defined benefit plans with an accumulated benefit obligation and projected benefit obligation in excess of plan assets
Accumulated benefit obligation	100.5	80.6
Projected benefit obligation	100.5	80.6
Fair value of plan assets	72.4	68.9
Components of net periodic benefit cost
Service cost	1.3	1.4	1.2
Interest cost	3.8	3.4	3.3
Expected return on plan assets	(5.1)	(4.4)	(4.0)
Curtailment/settlement expense			0.2
Prior service (credit) cost	0.2	0.2	0.2
Amortization of net loss	0.4	1.8	1.5
Net periodic benefit cost	0.6	2.4	2.4
Weighted average assumptions to determine net cost
Discount rate (as a percent)	4.70%	4.00%	4.25%
Expected long-term rate of return on plan assets (as a percent)	7.22%	7.30%	7.43%
Weighted average assumptions to determine benefit obligations
Discount rate (as a percent)	3.78%	4.70%
Expected long-term rate of return on plan assets (as a percent)	7.22%	7.30%
Expected employer contributions during 2015	1.5
Postretirement Medical Plan
Change in benefit obligation
Benefit obligation at beginning of year	9.9	10.1
Service cost	0.2	0.2	0.3
Interest cost	0.3	0.2
Actuarial (gain) loss	(1.6)	(0.4)
Benefits paid	(0.3)	(0.2)
Contributions by participants	0.1
Benefit obligation at end of year	8.6	9.9	10.1
Funded status
Funded status of the plans	(8.6)	(9.9)
Items not yet recognized as component of net periodic pension expense
Unrecognized net actuarial losses	1.3	3.4
Unamortized prior service (credit) cost	(4.5)	(6.3)
Accumulated other comprehensive (income) loss	(3.2)	(2.9)
Amounts recognized in the statement of financial position
Current liabilities	(0.7)	(0.7)
Noncurrent liabilities	(7.8)	(9.2)
Accumulated other comprehensive (income) loss	(3.2)	(2.9)
Net amount recognized	(11.7)	(12.8)
Components of net periodic benefit cost
Service cost	0.2	0.2	0.3
Interest cost	0.3	0.2	0.3
Prior service (credit) cost	(1.7)	(1.7)	(1.7)
Amortization of net loss	0.4	0.6	0.6
Net periodic benefit cost	$ (0.8)	$ (0.7)	$ (0.5)
Weighted average assumptions to determine net cost
Discount rate (as a percent)	3.10%	2.25%	3.53%
Health care cost trend rate (as a percent)	9.00%	9.00%	9.50%
Rate to which the cost trend rate is assumed to decline (as a percent)	4.25%	4.25%	4.50%
Year that the rate reaches the ultimate trend rate	2033	2032	2031
Weighted average assumptions to determine benefit obligations
Discount rate (as a percent)	2.50%	3.10%
Health care cost trend rate assumption for next year (as a percent)	8.50%	9.00%
Rate to which the cost trend rate is assumed to decline (as a percent)	4.25%	4.25%
Year that the rate reaches the ultimate trend rate	2034	2033

The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

No definition available.