Retirement and Postretirement Plans (Qualified Plan's Assets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Plan Assets
Fair value	$ 124.7	$ 120.8	$ 133.0
Qualified Plan
Plan Assets
Fair value	124.0	120.5
Asset allocations (as a percent)	100.00%	100.00%
Qualified Plan | Level 1 Inputs
Plan Assets
Fair value	87.6	75.3
Qualified Plan | Level 2 Inputs
Plan Assets
Fair value	36.4	45.2
Qualified Plan | Level 3 Inputs
Plan Assets
Fair value	0	0
Qualified Plan | Fixed maturity investments
Plan Assets
Fair value	1.9	2.4
Asset allocations (as a percent)	1.50%	2.00%
Qualified Plan | Fixed maturity investments | Level 1 Inputs
Plan Assets
Fair value	0	0
Qualified Plan | Fixed maturity investments | Level 2 Inputs
Plan Assets
Fair value	1.9	2.4
Qualified Plan | Fixed maturity investments | Level 3 Inputs
Plan Assets
Fair value	0	0
Qualified Plan | Common equity securities
Plan Assets
Fair value	79.5	72.2
Asset allocations (as a percent)	64.20%	59.90%
Qualified Plan | Common equity securities | Level 1 Inputs
Plan Assets
Fair value	79.5	72.2
Qualified Plan | Common equity securities | Level 2 Inputs
Plan Assets
Fair value	0	0
Qualified Plan | Common equity securities | Level 3 Inputs
Plan Assets
Fair value	0	0
Qualified Plan | Convertible fixed maturity investments
Plan Assets
Fair value	34.5	42.8
Asset allocations (as a percent)	27.80%	35.50%
Qualified Plan | Convertible fixed maturity investments | Level 1 Inputs
Plan Assets
Fair value	0	0
Qualified Plan | Convertible fixed maturity investments | Level 2 Inputs
Plan Assets
Fair value	34.5	42.8
Qualified Plan | Convertible fixed maturity investments | Level 3 Inputs
Plan Assets
Fair value	0	0
Qualified Plan | Cash
Plan Assets
Fair value	8.1	3.1
Asset allocations (as a percent)	6.50%	2.60%
Qualified Plan | Cash | Level 1 Inputs
Plan Assets
Fair value	8.1	3.1
Qualified Plan | Cash | Level 2 Inputs
Plan Assets
Fair value	0	0
Qualified Plan | Cash | Level 3 Inputs
Plan Assets
Fair value	$ 0	$ 0