Employee Benefit Plans (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-Based Compensation Expense
Total Share-Based Cost	$ 11.1	$ 12.7	$ 10.1
Less: Share-based compensation capitalized as DAC	3.0	1.8	2.3
Share-based compensation expense	8.1	10.9	7.8
Income tax benefit	1.6	2.3	1.8
Employee
Share-Based Compensation Expense
Total Share-Based Cost	10.2	11.8	9.1
Directors
Share-Based Compensation Expense
Total Share-Based Cost	0.9	0.9	1.0
Restricted Stock Awards | Employee
Share-Based Compensation Expense
Recurring amortization	0.2	1.3	2.8
Accelerated amortization for retirement eligible employees			0.3
Total Share-Based Cost	0.2	1.3	3.1
Restricted Stock Awards | Directors
Share-Based Compensation Expense
Total Share-Based Cost	0.8	0.6	0.6
Restricted Stock Units | Employee
Share-Based Compensation Expense
Recurring amortization	3.0	2.4	1.6
Accelerated amortization for retirement eligible employees	4.8	3.8	1.4
Total Share-Based Cost	7.8	6.2	3.0
Restricted Stock Units | Directors
Share-Based Compensation Expense
Total Share-Based Cost			0.2
Stock Options | Employee
Share-Based Compensation Expense
Recurring amortization	1.7	1.7	2.3
Accelerated amortization for retirement eligible employees	0.2	2.2	0.5
Total Share-Based Cost	1.9	3.9	2.8
Stock Options | Directors
Share-Based Compensation Expense
Total Share-Based Cost	0.1	0.3	0.2
Stock Purchase Plan
Share-Based Compensation Expense
Share-based compensation expense	0.2
Stock Purchase Plan | Employee
Share-Based Compensation Expense
Total Share-Based Cost	$ 0.3	$ 0.4	$ 0.2