CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Millions, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Net Unrealized Appreciation on Investments and Derivative Instruments:	Defined Benefit Pension and Postretirement Plans:	Cumulative Foreign Currency Translation Adjustment:	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Retained Earnings Balance previously reported	Retained Earnings Balance as adjusted	Treasury Stock
Balance at beginning of period (Cumulative effect of accounting change)								$ (19.5)
Balance at beginning of period at Dec. 31, 2009		0.6	1,808.5	107.7	(78.9)				1,141.1	1,121.6	(620.4)
Net income	151.2							151.2
Net actuarial loss arising in the period					(13.9)
Net appreciation during the period:
Net appreciation on available-for-sale securities and derivative instruments	130.7			104.7
Benefit (provision) for deferred income taxes	5.9			5.9
Unrealized gains arising during period	139.8			110.6
Settlement of accelerated share repurchases			(8.7)
Shares purchased at cost											(126.0)
Dividends to shareholders								(47.2)
Amortization during the period:
Amount recognized as net periodic benefit cost	(4.1)				9.8
Benefit for deferred income taxes	1.4				1.4
Total pension and postretirement benefits	(2.7)				(2.7)
Employee and director stock-based awards and other			(3.3)
Net shares reissued at cost under employee stock-based compensation plans											26.3
Treasury stock issued for less than cost								(9.7)
Recognition of employee stock-based compensation								7.8
Balance at end of period (Cumulative effect of accounting change)								(2.3)
Balance at end of period at Dec. 31, 2010	2,437.4	0.6	1,796.5	218.3	(81.6)		136.7	1,223.7	1,223.7	1,221.4	(720.1)
Net income	36.7							36.7
Net actuarial loss arising in the period					(16.0)
Net appreciation during the period:
Net appreciation on available-for-sale securities and derivative instruments	97.8			75.6
Benefit (provision) for deferred income taxes	14.8			14.8
Unrealized gains arising during period	121.3			90.4
Amount recognized as cumulative foreign currency translation during the year	(17.7)					(17.7)
Shares purchased at cost											(21.7)
Dividends to shareholders								(50.9)
Amortization during the period:
Amount recognized as net periodic benefit cost	(5.8)				10.2
Benefit for deferred income taxes	0.6				0.6
Total pension and postretirement benefits	(5.2)				(5.2)
Benefit (provision) for deferred income taxes	6.2					6.2
Employee and director stock-based awards and other			(11.7)
Net shares reissued at cost under employee stock-based compensation plans											18.7
Treasury stock issued for less than cost								(6.9)
Total cumulative foreign currency translation adjustment	(11.5)					(11.5)
Recognition of employee stock-based compensation								11.0
Balance at end of period at Dec. 31, 2011	2,484.0	0.6	1,784.8	308.7	(86.8)	(11.5)	210.4	1,211.3	1,211.3	1,211.3	(723.1)
Net income	55.9							55.9
Net actuarial loss arising in the period					(24.9)
Net appreciation during the period:
Net appreciation on available-for-sale securities and derivative instruments	186.4			163.5
Benefit (provision) for deferred income taxes	(46.2)			(46.2)
Unrealized gains arising during period	146.2			117.3
Amount recognized as cumulative foreign currency translation during the year	12.2					12.2
Shares purchased at cost											(20.0)
Dividends to shareholders								(55.1)
Amortization during the period:
Amount recognized as net periodic benefit cost	(15.6)				9.3
Benefit for deferred income taxes	5.8				5.8
Total pension and postretirement benefits	(9.8)				(9.8)
Benefit (provision) for deferred income taxes	(4.3)					(4.3)
Employee and director stock-based awards and other			2.3
Net shares reissued at cost under employee stock-based compensation plans											13.4
Treasury stock issued for less than cost								(6.0)
Total cumulative foreign currency translation adjustment	7.9					7.9
Recognition of employee stock-based compensation								5.5
Balance at end of period at Dec. 31, 2012	$ 2,595.4		$ 1,787.1	$ 426.0	$ (96.6)	$ (3.6)	$ 325.8	$ 1,211.6			$ (729.7)