Retirement and Postretirement Plans (Details 5) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Plan Assets
Fair value	$ 120.8	$ 133.0	$ 130.2
Qualified Plan
Plan Assets
Asset allocations (as a percent)	100.00%	100.00%
Fair value	120.5	132.7
Qualified Plan | Level 1 Inputs
Plan Assets
Fair value	75.3	76.5
Qualified Plan | Level 2 Inputs
Plan Assets
Fair value	45.2	56.2
Qualified Plan | Fixed maturity investments
Plan Assets
Asset allocations (as a percent)	2.00%	0.40%
Fair value	2.4	0.5
Qualified Plan | Fixed maturity investments | Level 2 Inputs
Plan Assets
Fair value	2.4	0.5
Qualified Plan | Common equity securities
Plan Assets
Asset allocations (as a percent)	59.90%	56.10%
Fair value	72.2	74.5
Qualified Plan | Common equity securities | Level 1 Inputs
Plan Assets
Fair value	72.2	74.5
Qualified Plan | Convertible fixed maturities
Plan Assets
Asset allocations (as a percent)	35.50%	42.00%
Fair value	42.8	55.7
Qualified Plan | Convertible fixed maturities | Level 2 Inputs
Plan Assets
Fair value	42.8	55.7
Qualified Plan | Cash
Plan Assets
Asset allocations (as a percent)	2.60%	1.50%
Fair value	3.1	2.0
Qualified Plan | Cash | Level 1 Inputs
Plan Assets
Fair value	$ 3.1	$ 2.0