Investments (Schedule of Amortized Cost and Fair Value of Fixed Maturity and Equity Securities) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2014	Dec. 31, 2013
Investment Holdings [Line Items]
Held for investment, amortized cost	$ 76,298	$ 76,255
Held for investment	64,920	60,840
Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	27,255,625	26,527,730
Available for sale, gross unrealized gains	1,459,316	928,699
Available for sale, gross unrealized losses	(399,468)	(845,982)
Available for sale securities, fair value	28,315,473	26,610,447
Equity Securities, Available For Sale [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	7,505	7,503
Available for sale, gross unrealized gains	262	275
Available for sale, gross unrealized losses	0	0
Available for sale securities, fair value	7,767	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	44,185	44,852
Available for sale, gross unrealized gains	325	367
Available for sale, gross unrealized losses	(1,210)	(2,294)
Available for sale securities, fair value	43,300	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	1,358,426	1,313,776
Available for sale, gross unrealized gains	8,276	1,875
Available for sale, gross unrealized losses	(67,248)	(121,362)
Available for sale securities, fair value	1,299,454	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	3,186,473	3,181,032
Available for sale, gross unrealized gains	265,511	164,785
Available for sale, gross unrealized losses	(14,671)	(39,074)
Available for sale securities, fair value	3,437,313	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	136,116	86,112
Available for sale, gross unrealized gains	10,379	8,907
Available for sale, gross unrealized losses	(2,472)	(3,462)
Available for sale securities, fair value	144,023	91,557
Corporate Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	17,662,806	17,142,118
Available for sale, gross unrealized gains	1,006,794	606,948
Available for sale, gross unrealized losses	(228,413)	(516,029)
Available for sale securities, fair value	18,441,187	17,233,037
Corporate Securities [Member] \| Fixed Maturity Securities [Member] \| Held For Investment Securities [Member]
Investment Holdings [Line Items]
Held for investment, amortized cost	76,298	76,255
Held for investment, gross unrealized gains	0	0
Held for investment, gross unrealized losses	(11,378)	(15,415)
Held for investment	64,920	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	1,831,161	1,895,913
Available for sale, gross unrealized gains	120,106	119,230
Available for sale, gross unrealized losses	(22,712)	(43,183)
Available for sale securities, fair value	1,928,555	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	2,003,425	1,821,988
Available for sale, gross unrealized gains	17,671	3,287
Available for sale, gross unrealized losses	(44,507)	(89,815)
Available for sale securities, fair value	1,976,589	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	1,033,033	1,041,939
Available for sale, gross unrealized gains	30,254	23,300
Available for sale, gross unrealized losses	(18,235)	(30,763)
Available for sale securities, fair value	$ 1,045,052	$ 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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