Investments (Summary Of Unrealized Appreciation (Depreciation) Of Available For Sale, Fixed Maturity And Equity Security Investments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 12,444,880	$ 11,731,173
Unrealized Appreciation	728,839	645,088
Unrealized Depreciation	(32,062)	(82,737)
Market Value	13,141,657	12,293,524
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	302,050	284,514
Unrealized Appreciation	11,079	16,407
Unrealized Depreciation	(1,007)	(287)
Market Value	312,122	300,634
State, Municipalities And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,214,990	1,558,615
Unrealized Appreciation	78,097	102,815
Unrealized Depreciation	(1,124)	(525)
Market Value	1,291,963	1,660,905
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,794,979	3,495,761
Unrealized Appreciation	247,439	197,914
Unrealized Depreciation	(7,098)	(27,054)
Market Value	4,035,320	3,666,621
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	169,615	186,936
Unrealized Appreciation	7,296	7,020
Unrealized Depreciation	(333)	(550)
Market Value	176,578	193,406
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	294,596	310,387
Unrealized Appreciation	27,965	20,942
Unrealized Depreciation	(2,473)	(9,902)
Market Value	320,088	321,427
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,091,672	2,198,937
Unrealized Appreciation	63,794	86,722
Unrealized Depreciation	(3,331)	(3,066)
Market Value	2,152,135	2,282,593
Non-agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,660	53,365
Unrealized Appreciation	590	499
Unrealized Depreciation	(201)	(775)
Market Value	8,049	53,089
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,785,738	1,555,707
Unrealized Appreciation	132,947	120,900
Unrealized Depreciation	(6,457)	(8,389)
Market Value	1,912,228	1,668,218
Foreign Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,783,580	2,086,951
Unrealized Appreciation	159,632	91,869
Unrealized Depreciation	(10,038)	(32,189)
Market Value	2,933,174	2,146,631
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	131,630	463,620
Unrealized Appreciation	11,864	4,060
Unrealized Depreciation	(1)	(18,750)
Market Value	$ 143,493	$ 448,930

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

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+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details