Consolidated Statements Of Changes In Shareholders' Equity (USD $) In Thousands, except Share data		Common Shares [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss), Net Of Deferred Income Taxes [Member]	Retained Earnings [Member]	Treasury Shares At Cost [Member]	Total
Balance at Dec. 31, 2008		$ 656	$ 1,824,552	$ (291,851)	$ 3,819,327	$ (392,329)
Balance, shares at Dec. 31, 2008		61,414,027
Issued during the period, net, shares		266,981
Issued during the period, net		2
Treasury shares acquired		(2,363,267)
Share-based compensation plans			20,592
Cumulative adjustment of initial adoption, net of tax	[1]			(57,312)	57,312
Other			37
Net increase (decrease) during the period				621,201			621,201
Net income (loss)					806,989		806,989
Dividends declared ($1.92 per share in 2011, 2010 and 2009)					(116,857)		(116,856)
Purchase of treasury shares						(190,597)
Balance at Dec. 31, 2009		658	1,845,181	272,038	4,566,771	(582,926)	6,101,722
Balance, shares at Dec. 31, 2009		59,317,741
Issued during the period, net, shares		175,999
Issued during the period, net		2
Treasury shares acquired		(5,065,572)
Share-based compensation plans			17,850
Net increase (decrease) during the period				60,220			60,220
Net income (loss)					610,754		610,754
Dividends declared ($1.92 per share in 2011, 2010 and 2009)					(108,477)		(108,477)
Purchase of treasury shares						(398,554)
Balance at Dec. 31, 2010		660	1,863,031	332,258	5,069,048	(981,480)	6,283,517
Balance, shares at Dec. 31, 2010		54,428,168					66,017,000
Issued during the period, net, shares		437,427
Issued during the period, net		5
Treasury shares acquired		(1,130,044)
Share-based compensation plans			29,957
Net increase (decrease) during the period				34,720			34,720
Net income (loss)					(80,486)		(80,486)
Dividends declared ($1.92 per share in 2011, 2010 and 2009)					(103,848)		(103,848)
Purchase of treasury shares						(92,490)
Balance at Dec. 31, 2011		$ 665	$ 1,892,988	$ 366,978	$ 4,884,714	$ (1,073,970)	$ 6,071,375
Balance, shares at Dec. 31, 2011		53,735,551					66,455,000

[1] The cumulative adjustment to accumulated other comprehensive income (loss), net of deferred income taxes, and retained earnings, represents the effect of initially adopting new guidance for other-than-temporary impairments of debt securities.