Summary of Investments - SOI Fixed Maturity AFS and non-credit OTTI in AOCI (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2015		Dec. 31, 2014
Securities available-for-sale
Total fixed maturities	$ 17,112,911		$ 18,953,144
Fixed maturities available-for-sale:	17,977,077		20,162,078
Fixed maturities
Securities available-for-sale
Total fixed maturities	17,112,911		18,953,144
Gross unrealized gains	1,056,109		1,310,377
Gross unrealized losses	191,943		101,443
Fixed maturities available-for-sale:	17,977,077		20,162,078
OTTI (gain) loss included in AOCI	(97,440)	[1]	(99,016)	[2]
U.S. government direct obligations and U.S. agencies
Securities available-for-sale
Total fixed maturities	874,239		3,478,153
Gross unrealized gains	56,416		70,597
Gross unrealized losses	2,957		1,494
Fixed maturities available-for-sale:	927,698		3,547,256
OTTI (gain) loss included in AOCI	0	[1]	0	[2]
Obligations of U.S. states and their subdivisions
Securities available-for-sale
Total fixed maturities	2,082,123		1,885,715
Gross unrealized gains	246,232		287,668
Gross unrealized losses	16,451		899
Fixed maturities available-for-sale:	2,311,904		2,172,484
OTTI (gain) loss included in AOCI	0	[1]	0	[2]
Foreign government securities
Securities available-for-sale
Total fixed maturities	2,373		2,455
Gross unrealized gains	8		0
Gross unrealized losses	0		4
Fixed maturities available-for-sale:	2,381		2,451
OTTI (gain) loss included in AOCI	0	[1]	0	[2]
Corporate debt securities
Securities available-for-sale
Total fixed maturities	11,819,023	[3]	11,258,517	[4]
Gross unrealized gains	584,963	[3]	763,036	[4]
Gross unrealized losses	152,896	[3]	82,104	[4]
Fixed maturities available-for-sale:	12,251,090	[3]	11,939,449	[4]
OTTI (gain) loss included in AOCI	(2,126)	[1],[3]	(2,228)	[2],[4]
Perpetual debt investments
Securities available-for-sale
Total fixed maturities	157,742		157,742
Fixed maturities available-for-sale:	129,537		131,799
Asset-backed securities
Securities available-for-sale
Total fixed maturities	1,244,518		1,263,089
Gross unrealized gains	139,173		149,152
Gross unrealized losses	10,857		13,702
Fixed maturities available-for-sale:	1,372,834		1,398,539
OTTI (gain) loss included in AOCI	(95,164)	[1]	(96,603)	[2]
Residential mortgage-backed securities
Securities available-for-sale
Total fixed maturities	143,205		167,793
Gross unrealized gains	5,963		7,368
Gross unrealized losses	1,980		1,932
Fixed maturities available-for-sale:	147,188		173,229
OTTI (gain) loss included in AOCI	(150)	[1]	(185)	[2]
Commercial mortgage-backed securities
Securities available-for-sale
Total fixed maturities	937,893		886,748
Gross unrealized gains	23,354		32,556
Gross unrealized losses	6,800		1,099
Fixed maturities available-for-sale:	954,447		918,205
OTTI (gain) loss included in AOCI	0	[1]	0	[2]
Collateralized debt obligations
Securities available-for-sale
Total fixed maturities	9,537		10,674
Gross unrealized gains	0		0
Gross unrealized losses	2		209
Fixed maturities available-for-sale:	9,535		10,465
OTTI (gain) loss included in AOCI	$ 0	[1]	$ 0	[2]

[1] Indicates the amount of any OTTI (gain) loss included in AOCI that is included in gross unrealized gains and losses. OTTI (gain) loss included in AOCI, as presented above, includes both the initial recognition of non-credit losses and the effects of subsequent increases and decreases in estimated fair value for those fixed maturity securities with previous non-credit impairment. The non-credit loss component of OTTI (gain) loss was in an unrealized gain position due to increases in estimated fair value subsequent to initial recognition of non-credit losses on such securities.

[2] Indicates the amount of any OTTI (gain) loss included in AOCI that is included in gross unrealized gains and losses. OTTI (gain) loss included in AOCI, as presented above, includes both the initial recognition of non-credit losses and the effects of subsequent increases and decreases in estimated fair value for those fixed maturity securities with previous non-credit impairment. The non-credit loss component of OTTI (gain) loss was in an unrealized gain position due to increases in estimated fair value subsequent to initial recognition of non-credit losses on such securities.

[3] Includes perpetual debt investments with amortized cost of $157,742 and estimated fair value of $129,537.

[4] Includes perpetual debt investments with amortized cost of $157,742 and estimated fair value of $131,799.