Investments (Schedule of Amortized Cost and Fair Value of Fixed Maturity and Equity Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Held for investment, amortized cost	$ 76,574	$ 76,432
Held for investment	62,000	75,838
Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	34,058,330	30,205,046
Available for sale, gross unrealized gains	1,815,380	2,395,577
Available for sale, gross unrealized losses	(483,868)	(155,421)
Available for sale, fair value	35,389,842	32,445,202
Equity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	7,514	7,509
Available for sale, gross unrealized gains	319	296
Available for sale, gross unrealized losses	0	0
Available for sale, fair value	7,833	7,805
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	36,355	137,710
Available for sale, gross unrealized gains	1,437	765
Available for sale, gross unrealized losses	(111)	(15)
Available for sale, fair value	37,681	138,460
United States Government Sponsored Agencies [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	1,286,586	1,364,424
Available for sale, gross unrealized gains	35,864	43,399
Available for sale, gross unrealized losses	(7,702)	(13,933)
Available for sale, fair value	1,314,748	1,393,890
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	3,405,519	3,293,551
Available for sale, gross unrealized gains	363,590	430,469
Available for sale, gross unrealized losses	(8,221)	(711)
Available for sale, fair value	3,760,888	3,723,309
Foreign Government Obligations [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	210,941	181,128
Available for sale, gross unrealized gains	16,199	16,628
Available for sale, gross unrealized losses	(10,153)	(3,953)
Available for sale, fair value	216,987	193,803
Corporate Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	22,738,792	19,984,747
Available for sale, gross unrealized gains	1,135,974	1,628,941
Available for sale, gross unrealized losses	(415,018)	(123,396)
Available for sale, fair value	23,459,748	21,490,292
Corporate Securities [Member] \| Fixed Maturity Securities [Member] \| Held For Investment Securities [Member]
Investment Holdings [Line Items]
Held for investment, amortized cost	76,574	76,432
Held for investment, gross unrealized gains	0	0
Held for investment, gross unrealized losses	(14,574)	(594)
Held for investment	62,000	75,838
Residential Mortgage Backed Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	1,431,656	1,616,846
Available for sale, gross unrealized gains	126,485	136,704
Available for sale, gross unrealized losses	(1,833)	(2,205)
Available for sale, fair value	1,556,308	1,751,345
Commercial Mortgage Backed Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	3,881,487	2,720,294
Available for sale, gross unrealized gains	90,536	90,649
Available for sale, gross unrealized losses	(30,160)	(3,323)
Available for sale, fair value	3,941,863	2,807,620
Other Asset Backed Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale Securities [Member]
Investment Holdings [Line Items]
Available for sale, amortized cost	1,066,994	906,346
Available for sale, gross unrealized gains	45,295	48,022
Available for sale, gross unrealized losses	(10,670)	(7,885)
Available for sale, fair value	$ 1,101,619	$ 946,483

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

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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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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