Consolidated Statements of Shareholders' Equity (USD $) In Millions	Preferred Stock [Member]	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss), net of tax	Net Unrealized Appreciation on Investments and Derivative Instruments:	Defined Benefit Pension and Postretirement Plans:	Cumulative Foreign Currency Translation Adjustment:	Retained Earnings	Treasury Stock	Total
Balance at beginning of period at Dec. 31, 2012		$ 0.6	$ 1,787.1		$ 426.0	$ (96.6)	$ (3.6)	$ 1,211.6	$ (729.7)
Net income								119.6		119.6
Shares purchased at cost									(72.3)
Employee and director stock-based awards and other			6.0
Net appreciation on available-for-sale securities and derivative instruments					(132.0)					(132.0)
Net amount recognized as net periodic benefit cost						6.0
Amount recognized as cumulative foreign currency translation during the period							(10.1)			(10.1)
Dividends to shareholders								(29.3)
Total accumulated other comprehensive income										(136.1)
Net shares reissued at cost under employee stock-based compensation plans									31.9
Stock-based compensation								(19.5)
Balance at end of period at Jun. 30, 2013		0.6	1,793.1	189.7	294.0	(90.6)	(13.7)	1,282.4	(770.1)	2,495.7
Balance at beginning of period at Dec. 31, 2013		0.6	1,830.1		259.3	(76.1)	(5.6)	1,349.1	(762.9)	2,594.5
Net income								137.2		137.2
Shares purchased at cost									(6.7)
Employee and director stock-based awards and other			(5.6)
Net appreciation on available-for-sale securities and derivative instruments					83.1					83.1
Net amount recognized as net periodic benefit cost						3.4
Amount recognized as cumulative foreign currency translation during the period							3.0			3.0
Dividends to shareholders								(32.6)
Total accumulated other comprehensive income										89.5
Net shares reissued at cost under employee stock-based compensation plans									20.8
Stock-based compensation								(2.0)
Balance at end of period at Jun. 30, 2014		$ 0.6	$ 1,824.5	$ 267.1	$ 342.4	$ (72.7)	$ (2.6)	$ 1,451.7	$ (748.8)	$ 2,795.1