Employee Share-Based Incentive Compensation Plans (Performance Shares) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Expense amortized
Expense recognized	$ (1.4)		$ (1.2)
Long Term Incentive Plan | Performance shares
Activity in plan
Beginning of period (in shares)	493,421		563,190
Payments and deferrals (in shares)	(142,138)	[1]	(238,658)	[1]
New awards (in shares)	165,800		179,000
Forfeitures and net change in assumed forfeitures (in shares)	(4,145)		(13,665)
End of period (in shares)	512,938		489,867
Expense amortized
Accrued expense at beginning of period	4.0		1.2
Payments and deferrals	(1.0)	[1]	0	[1]
Forfeitures and net change in assumed forfeitures	0		0
Expense recognized	(0.6)		(0.4)
Accrued expense at end of period	3.6		1.6
Additional disclosures
Target OB Performance Shares outstanding	512,938
Assumed forfeitures (in shares)	(13,152)
Assumed forfeitures	(0.1)
Additional compensation cost that would be recognized if all outstanding performance shares vested	4.7
Long Term Incentive Plan | Performance shares | Performance cycle 2011 - 2013
Additional disclosures
Growth target percentage	37.10%
Long Term Incentive Plan | Performance shares | Performance cycle 2012 - 2014
Expense amortized
Accrued expense at end of period	2.3
Additional disclosures
Target OB Performance Shares outstanding	181,290
Long Term Incentive Plan | Performance shares | Performance cycle 2013 - 2015
Expense amortized
Accrued expense at end of period	1.2
Additional disclosures
Target OB Performance Shares outstanding	179,000
Long Term Incentive Plan | Performance shares | Performance cycle 2014 - 2016
Expense amortized
Accrued expense at end of period	0.2
Additional disclosures
Target OB Performance Shares outstanding	165,800
Long Term Incentive Plan | Performance shares | Performance cycle 2012 - 2016
Expense amortized
Accrued expense at end of period	$ 3.7
Additional disclosures
Target OB Performance Shares outstanding	526,090
Long Term Incentive Plan | Performance shares | Performance Cycle 2010 To 2012
Additional disclosures
Growth target percentage	0.00%

[1] Performance share payments in 2014 for the 2011-2013 performance cycle were based upon a performance factor of 37.1%. No payments were made in 2013 for the 2010-2012 performance cycle as the performance factor was zero.