Employee Benefit Plans - Reconciliation of Pension Plan Investments Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Actual return on plan assets [Abstract]
Fair value of plan assets at end of year	$ 160.8	$ 153.4
Pension Benefits
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year			142.3
Actual return on plan assets [Abstract]
Fair value of plan assets at end of year	160.8	153.4	142.3
Real estate partnership interests
Actual return on plan assets [Abstract]
Fair value of plan assets at end of year		7.5
Private Equity
Actual return on plan assets [Abstract]
Fair value of plan assets at end of year	0.3	0.3
Insurance
Actual return on plan assets [Abstract]
Fair value of plan assets at end of year	1.4	1.0
Significant Un-observable Inputs (Level 3)
Actual return on plan assets [Abstract]
Fair value of plan assets at end of year	1.7	15.2
Significant Un-observable Inputs (Level 3) | Pension Benefits
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	15.2	9.4
Actual return on plan assets [Abstract]
Assets held at the reporting date	0.4	1.3
Assets sold during the period	0	0.4
Purchases, sales and settlements	(13.9)	4.1
Fair value of plan assets at end of year	1.7	15.2
Significant Un-observable Inputs (Level 3) | Real estate partnership interests
Actual return on plan assets [Abstract]
Fair value of plan assets at end of year		7.5
Significant Un-observable Inputs (Level 3) | Real estate partnership interests | Pension Benefits
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	7.5	7.8
Actual return on plan assets [Abstract]
Assets held at the reporting date	0	1.1
Assets sold during the period	0	0.3
Purchases, sales and settlements	(7.5)	(1.7)
Fair value of plan assets at end of year	0	7.5
Significant Un-observable Inputs (Level 3) | Private Equity
Actual return on plan assets [Abstract]
Fair value of plan assets at end of year	0.3	0.3
Significant Un-observable Inputs (Level 3) | Private Equity | Pension Benefits
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	0.3	0.7
Actual return on plan assets [Abstract]
Assets held at the reporting date	0	(0.2)
Assets sold during the period	0	0.1
Purchases, sales and settlements	0	(0.3)
Fair value of plan assets at end of year	0.3	0.3
Significant Un-observable Inputs (Level 3) | Insurance
Actual return on plan assets [Abstract]
Fair value of plan assets at end of year	1.4	1.0
Significant Un-observable Inputs (Level 3) | Insurance | Pension Benefits
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	1.0	0.9
Actual return on plan assets [Abstract]
Assets held at the reporting date	0.4	0.1
Assets sold during the period	0	0
Purchases, sales and settlements	0	0
Fair value of plan assets at end of year	1.4	1.0
Significant Un-observable Inputs (Level 3) | Limited Partnership | Pension Benefits
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	6.4	0
Actual return on plan assets [Abstract]
Assets held at the reporting date	0	0.3
Assets sold during the period	0	0
Purchases, sales and settlements	(6.4)	6.1
Fair value of plan assets at end of year	$ 0	$ 6.4