Investments (Gross Unrealized Losses on Investments, By Category and Length of Time) (Details) (Fixed Maturity Securities [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	$ 2,346,226	$ 11,635,998
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	(56,929)	(741,947)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	2,731,950	1,097,643
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(98,492)	(104,035)
Available for sale, continuous unrealized loss position, total, fair value	5,078,176	12,733,641
Available for sale, continuous unrealized loss position, total, unrealized losses	(155,421)	(845,982)
United States Government Full Faith and Credit [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	0	32,969
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	0	(2,294)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	498	0
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(15)	0
Available for sale, continuous unrealized loss position, total, fair value	498	32,969
Available for sale, continuous unrealized loss position, total, unrealized losses	(15)	(2,294)
United States Government Sponsored Agencies [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	0	692,320
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	0	(88,671)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	610,339	467,309
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(13,933)	(32,691)
Available for sale, continuous unrealized loss position, total, fair value	610,339	1,159,629
Available for sale, continuous unrealized loss position, total, unrealized losses	(13,933)	(121,362)
United States Municipalities, States and Territories [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	0	614,056
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	0	(39,074)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	27,947	0
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(711)	0
Available for sale, continuous unrealized loss position, total, fair value	27,947	614,056
Available for sale, continuous unrealized loss position, total, unrealized losses	(711)	(39,074)
Foreign Government Obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	14,194	26,298
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	(1,068)	(3,462)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	11,542	0
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(2,885)	0
Available for sale, continuous unrealized loss position, total, fair value	25,736	26,298
Available for sale, continuous unrealized loss position, total, unrealized losses	(3,953)	(3,462)
Corporate Securities [Member] \| Finance, Insurance and Real Estate [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	253,439	1,690,846
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	(2,586)	(92,426)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	399,874	153,037
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(16,277)	(12,873)
Available for sale, continuous unrealized loss position, total, fair value	653,313	1,843,883
Available for sale, continuous unrealized loss position, total, unrealized losses	(18,863)	(105,299)
Corporate Securities [Member] \| Manufacturing, Construction and Mining [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	1,078,089	3,370,775
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	(35,151)	(191,245)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	694,088	93,608
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(35,926)	(16,088)
Available for sale, continuous unrealized loss position, total, fair value	1,772,177	3,464,383
Available for sale, continuous unrealized loss position, total, unrealized losses	(71,077)	(207,333)
Corporate Securities [Member] \| Utilities and Related Sectors [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	373,952	1,829,868
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	(8,185)	(102,758)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	344,313	83,550
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(10,153)	(11,547)
Available for sale, continuous unrealized loss position, total, fair value	718,265	1,913,418
Available for sale, continuous unrealized loss position, total, unrealized losses	(18,338)	(114,305)
Corporate Securities [Member] \| Wholesale/Retail Trade [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	88,766	428,407
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	(2,290)	(25,189)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	99,427	17,687
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(3,122)	(1,992)
Available for sale, continuous unrealized loss position, total, fair value	188,193	446,094
Available for sale, continuous unrealized loss position, total, unrealized losses	(5,412)	(27,181)
Corporate Securities [Member] \| Services, Media and Other [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	131,940	834,699
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	(1,567)	(51,508)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	277,296	107,242
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(8,139)	(10,403)
Available for sale, continuous unrealized loss position, total, fair value	409,236	941,941
Available for sale, continuous unrealized loss position, total, unrealized losses	(9,706)	(61,911)
Corporate Securities [Member] \| Insurance [Member]
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Held for investment, continuous unrealized loss position, less than 12 months, fair value	0	0
Held for investment, continuous unrealized loss position, less than 12 months, unrealized losses	0	0
Held for investment, continuous unrealized loss position, 12 months or more, fair value	75,838	60,840
Held for investment, continuous unrealized loss position, 12 months or more, unrealized losses	(594)	(15,415)
Held for investment, continuous unrealized loss position, total, fair value	75,838	60,840
Held for investment, continuous unrealized loss position, total, unrealized losses	594	15,415
Residential Mortgage Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	22,115	309,599
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	(1,219)	(41,080)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	20,427	31,739
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(986)	(2,103)
Available for sale, continuous unrealized loss position, total, fair value	42,542	341,338
Available for sale, continuous unrealized loss position, total, unrealized losses	(2,205)	(43,183)
Commercial Mortgage Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	241,637	1,450,143
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	(1,344)	(83,814)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	187,241	51,099
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(1,979)	(6,001)
Available for sale, continuous unrealized loss position, total, fair value	428,878	1,501,242
Available for sale, continuous unrealized loss position, total, unrealized losses	(3,323)	(89,815)
Other Asset Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale, continuous unrealized loss position, less than 12 months, fair value	142,094	356,018
Available for sale, continuous unrealized loss position, less than 12 months, unrealized losses	(3,519)	(20,426)
Available for sale, continuous unrealized loss position, 12 months or more, fair value	58,958	92,372
Available for sale, continuous unrealized loss position, 12 months or more, unrealized losses	(4,366)	(10,337)
Available for sale, continuous unrealized loss position, total, fair value	201,052	448,390
Available for sale, continuous unrealized loss position, total, unrealized losses	$ (7,885)	$ (30,763)

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

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This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for twelve months or longer.

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