Consolidated Statements Of Shareholders' Equity (USD $) In Millions, unless otherwise specified	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 [Member]	Cumulative Foreign Currency Translation Adjustment [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Beginning balance at Dec. 31, 2010		$ 0.6	$ 1,796.5	$ 218.3	$ (81.6)			$ 1,246.8	$ (720.1)
Employee and director stock-based awards and other			(16.5)
Amount recognized as net periodic benefit cost during the period					2.6					2.6
Provision for deferred income taxes					(0.9)					(0.9)
Total pension and postretirement benefits					1.7					1.7
Net shares reissued at cost under employee stock-based compensation plans									15.8
Net income								29.3		29.3
Net appreciation during the period:
Net appreciation on available-for-sale securities and derivative instruments				3.5
Benefit (provision) for deferred income taxes				3.1
Total available-for-sale securities				6.6
Dividends to shareholders								(12.5)
Treasury stock issued for less than cost								(5.6)
Recognition of employee stock-based compensation								9.4
Cumulative effect of accounting change, net of taxes								(23.1)
Balance at beginning of period, as adjusted								1,223.7
Ending balance at Mar. 31, 2011		0.6	1,780.0	224.9	(79.9)	145.0		1,244.3	(704.3)	2,465.6
Beginning balance at Dec. 31, 2011		0.6	1,784.8	308.7	(86.8)		(11.5)	1,211.3	(723.1)	2,484.0
Employee and director stock-based awards and other			(4.7)
Amount recognized as net periodic benefit cost during the period					2.3					2.3
Provision for deferred income taxes					(0.8)					(0.8)
Total pension and postretirement benefits					1.5					1.5
Amount recognized as cumulative foreign currency translation during the period							14.3			14.3
Provision for deferred income taxes							(5.0)			(5.0)
Total cumulative foreign currency translation adjustment							9.3			9.3
Net shares reissued at cost under employee stock-based compensation plans									7.5
Net income								49.7		49.7
Net appreciation during the period:
Net appreciation on available-for-sale securities and derivative instruments				68.2
Benefit (provision) for deferred income taxes				(24.3)
Total available-for-sale securities				43.9
Dividends to shareholders								(13.5)
Treasury stock issued for less than cost								(3.0)
Recognition of employee stock-based compensation								4.3
Balance at beginning of period, as adjusted								1,211.3
Ending balance at Mar. 31, 2012		$ 0.6	$ 1,780.1	$ 352.6	$ (85.3)	$ 265.1	$ (2.2)	$ 1,248.8	$ (715.6)	$ 2,579.0