Consolidated Statements of Shareholders' Equity (USD $) In Millions	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Net Unrealized Appreciation on Investments and Derivative Instruments [Member]	Defined Benefit Pension and Postretirement Plans [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Beginning balance at Dec. 31, 2009		$ 0.6	$ 1,808.5	$ 107.7	$ (78.9)		$ 1,141.1	$ (620.4)
Shares purchased at cost								(126.0)
Employee and director stock-based awards and other			(11.8)
Amount recognized as net periodic benefit cost during the period					4.9				4.9
Provision for deferred federal income taxes					(1.7)				(1.7)
Total pension and postretirement benefits					3.2				3.2
Net shares reissued at cost under employee stock-based compensation plans								11.5
Net (loss) income							44.1		44.1
Net appreciation during the period:
Net appreciation on available-for-sale securities and derivative instruments				125.7
Benefit (provision) for deferred federal income taxes				(31.5)
Total available-for-sale securities				94.2
Dividends to shareholders							(24.3)
Treasury stock issued for less than cost							(4.6)
Recognition of share-based compensation							6.7
Ending balance at Jun. 30, 2010		0.6	1,796.7	201.9	(75.7)	126.2	1,163.0	(734.9)	2,351.6
Beginning balance at Dec. 31, 2010		0.6	1,796.5	218.3	(81.6)		1,246.8	(720.1)	2,460.5
Employee and director stock-based awards and other			(14.0)
Amount recognized as net periodic benefit cost during the period					5.1				5.1
Provision for deferred federal income taxes					(1.8)				(1.8)
Total pension and postretirement benefits					3.3				3.3
Net shares reissued at cost under employee stock-based compensation plans								16.6
Net (loss) income							(2.5)		(2.5)
Net appreciation during the period:
Net appreciation on available-for-sale securities and derivative instruments				41.0
Benefit (provision) for deferred federal income taxes				1.5
Total available-for-sale securities				42.5
Dividends to shareholders							(25.0)
Treasury stock issued for less than cost							(5.9)
Recognition of share-based compensation							9.5
Ending balance at Jun. 30, 2011		$ 0.6	$ 1,782.5	$ 260.8	$ (78.3)	$ 182.5	$ 1,222.9	$ (703.5)	$ 2,485.0