Schedule 2 - Parent Company Financial Statements - Statements of Cash Flows (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Activities:
Net Income	$ 103.4	$ 74.5	$ 177.9
Adjustment Required to Reconcile Net Income to Net Cash Provided by Operations:
Net Realized (Gains) Losses on Sales of Investments	(65.4)	(33.7)	(42.6)
Other, Net	33.4	30.4	19.1
Net Cash Provided by Operating Activities	65.7	(25.0)	58.5
Investing Activities:
Sales and Maturities of Fixed Maturities	914.4	650.3	706.7
Purchases of Fixed Maturities	(872.6)	(663.4)	(532.1)
Change in Short-term Investments	(80.0)	155.5	(7.3)
Net Cash Provided (Used) by Investing Activities	(106.2)	564.6	319.3
Notes Payable Payments:
Cash Dividends Paid	(56.9)	(58.2)	(54.6)
Common Stock Repurchases	(60.7)	(27.4)	(34.4)
Cash Exercise of Stock Options	1.3	0.2	0.5
Excess Tax Benefits on Share-based Awards	0.5	0.2	0.2
Net Cash Used by Financing Activities	(114.4)	(405.6)	(404.3)
Increase (Decrease) in Cash	(154.9)	134.0	(26.5)
Cash, Beginning of Year	251.2	117.2	143.7
Cash, End of Period	96.3	251.2	117.2
Parent Company [Member]
Operating Activities:
Net Income	103.4	74.5	177.9
Adjustment Required to Reconcile Net Income to Net Cash Provided by Operations:
Equity in Net Income of Subsidiaries	(137.8)	(105.4)	(201.1)
Cash Dividends from Subsidiaries	95.0	70.8	147.4
Cash Contribution to Defined Benefit Plan	0	(32.2)	(15.0)
Net Realized (Gains) Losses on Sales of Investments	(0.3)	0.2	(0.5)
Other, Net	8.5	35.5	(10.8)
Net Cash Provided by Operating Activities	68.8	43.4	97.9
Investing Activities:
Capital Contributed to Subsidiaries	0	0	(110.0)
Capital Distribution from Subsidiary	20.0	250.0	0
Maturity of Note Receivable from Subsidiary	0	0	20.0
Sales and Maturities of Fixed Maturities	13.1	0	0
Purchases of Fixed Maturities	0	0	(13.1)
Purchases of Common Stocks from Subsidiary	0	(50.8)	0
Change in Short-term Investments	(106.3)	(35.4)	10.5
Net Cash Provided (Used) by Investing Activities	(73.2)	163.8	(92.6)
Notes Payable Proceeds:
Senior Notes Payable Issued	0	0	247.8
Revolving Credit Agreement	0	95.0	140.0
Notes Payable Payments:
Senior Notes Payable Repaid	0	0	(200.0)
Revolving Credit Agreement	0	(95.0)	(140.0)
Cash Dividends Paid	(56.9)	(58.2)	(54.6)
Common Stock Repurchases	(60.7)	(27.4)	(34.4)
Cash Exercise of Stock Options	1.3	0.2	0.5
Excess Tax Benefits on Share-based Awards	0.5	0.2	0.2
Net Cash Used by Financing Activities	(115.8)	(85.2)	(40.5)
Increase (Decrease) in Cash	(120.2)	122.0	(35.2)
Cash, Beginning of Year	122.4	0.4	35.6
Cash, End of Period	$ 2.2	$ 122.4	$ 0.4