Investments (Schedule of Amortized Cost and Fair Value of Fixed Maturity and Equity Securities) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2014	Dec. 31, 2013
Investment Holdings [Line Items]
Held for investment, amortized cost	$ 76,342	$ 76,255
Held for investment	66,571	60,840
Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	27,540,945	26,527,730
Available for sale, gross unrealized gains	1,959,362	928,699
Available for sale, gross unrealized losses	(182,735)	(845,982)
Available for sale securities, fair value	29,317,572	26,610,447
Equity Securities, Available For Sale [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	7,506	7,503
Available for sale, gross unrealized gains	256	275
Available for sale, gross unrealized losses	0	0
Available for sale securities, fair value	7,762	7,778
United States Government Full Faith and Credit [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	38,590	44,852
Available for sale, gross unrealized gains	310	367
Available for sale, gross unrealized losses	(417)	(2,294)
Available for sale securities, fair value	38,483	42,925
United States Government Sponsored Agencies [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	1,199,787	1,313,776
Available for sale, gross unrealized gains	21,181	1,875
Available for sale, gross unrealized losses	(35,627)	(121,362)
Available for sale securities, fair value	1,185,341	1,194,289
United States Municipalities, States and Territories [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	3,188,026	3,181,032
Available for sale, gross unrealized gains	324,759	164,785
Available for sale, gross unrealized losses	(6,587)	(39,074)
Available for sale securities, fair value	3,506,198	3,306,743
Foreign Government Obligations [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	181,120	86,112
Available for sale, gross unrealized gains	13,335	8,907
Available for sale, gross unrealized losses	(1,492)	(3,462)
Available for sale securities, fair value	192,963	91,557
Corporate Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	17,916,567	17,142,118
Available for sale, gross unrealized gains	1,371,622	606,948
Available for sale, gross unrealized losses	(100,814)	(516,029)
Available for sale securities, fair value	19,187,375	17,233,037
Corporate Securities [Member] \| Fixed Maturity Securities [Member] \| Held For Investment Securities [Member]
Investment Holdings [Line Items]
Held for investment, amortized cost	76,342	76,255
Held for investment, gross unrealized gains	0	0
Held for investment, gross unrealized losses	(9,771)	(15,415)
Held for investment	66,571	60,840
Residential Mortgage Backed Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	1,747,233	1,895,913
Available for sale, gross unrealized gains	137,213	119,230
Available for sale, gross unrealized losses	(13,881)	(43,183)
Available for sale securities, fair value	1,870,565	1,971,960
Commercial Mortgage Backed Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	2,249,396	1,821,988
Available for sale, gross unrealized gains	56,897	3,287
Available for sale, gross unrealized losses	(10,197)	(89,815)
Available for sale securities, fair value	2,296,096	1,735,460
Other Asset Backed Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	1,020,226	1,041,939
Available for sale, gross unrealized gains	34,045	23,300
Available for sale, gross unrealized losses	(13,720)	(30,763)
Available for sale securities, fair value	$ 1,040,551	$ 1,034,476

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

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Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

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Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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Amount of unrecognized gain before loss on investments in held-to-maturity securities.

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Amount of unrecognized loss before gain on investments in held-to-maturity securities. Excludes write-down for other than temporary impairment (OTTI).

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