CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $) In Millions, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Net Unrealized Appreciation (Depreciation) on Investments and Derivative Instruments:	Defined Benefit Pension and Postretirement Plans:	Cumulative Foreign Currency Translation Adjustment:	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Balance at beginning of period at Dec. 31, 2011		$ 0.6	$ 1,784.8	$ 308.7	$ (86.8)	$ (11.5)		$ 1,211.3	$ (723.1)
Net income	49.7							49.7
Net appreciation during the period:
Net appreciation on available-for-sale securities and derivative instruments	40.9			43.9
Employee and director stock-based awards and other			(4.7)
Amortization recognized as net periodic benefit cost	1.5				1.5
Amount recognized as cumulative foreign currency translation during the period	9.3					9.3
Dividends to shareholders								(13.5)
Net shares reissued at cost under employee stock-based compensation plans									7.5
Stock-based compensation								1.3
Balance at end of period at Mar. 31, 2012	2,579.0	0.6	1,780.1	352.6	(85.3)	(2.2)	265.1	1,248.8	(715.6)
Balance at beginning of period at Dec. 31, 2012	2,595.4	0.6	1,787.1	426.0	(96.6)	(3.6)		1,211.6	(729.7)
Net income	66.2							66.2
Net appreciation during the period:
Net appreciation on available-for-sale securities and derivative instruments	5.5			5.4
Shares purchased at cost									(25.2)
Employee and director stock-based awards and other			(1.8)
Amortization recognized as net periodic benefit cost	1.9				1.9
Amount recognized as cumulative foreign currency translation during the period	(10.0)					(10.0)
Dividends to shareholders								(14.8)
Net shares reissued at cost under employee stock-based compensation plans									17.1
Stock-based compensation								(10.2)
Balance at end of period at Mar. 31, 2013	$ 2,624.0	$ 0.6	$ 1,785.3	$ 431.4	$ (94.7)	$ (13.6)	$ 323.1	$ 1,252.8	$ (737.8)