SOI Fixed Maturity AFS and non-credit OTTI in AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014
Securities available-for-sale
Total fixed maturities	$ 20,007,462		$ 18,953,144
Fixed maturities, available-for-sale	20,531,627		20,162,078
Fixed maturities
Securities available-for-sale
Total fixed maturities	20,007,462		18,953,144
Gross unrealized gains	883,519		1,310,377
Gross unrealized losses	359,354		101,443
Fixed maturities, available-for-sale	20,531,627		20,162,078
OTTI (gain) loss included in AOCI	(88,357)	[1]	(99,016)	[2]
U.S. government direct obligations and U.S. agencies
Securities available-for-sale
Total fixed maturities	3,291,167		3,478,153
Gross unrealized gains	55,193		70,597
Gross unrealized losses	4,608		1,494
Fixed maturities, available-for-sale	3,341,752		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	1,988,214		1,885,715
Gross unrealized gains	238,862		287,668
Gross unrealized losses	7,903		899
Fixed maturities, available-for-sale	2,219,173		2,172,484
OTTI (gain) loss included in AOCI	50	[1]	0	[2]
Foreign government securities
Securities available-for-sale
Total fixed maturities	2,291		2,455
Gross unrealized gains	0		0
Gross unrealized losses	5		4
Fixed maturities, available-for-sale	2,286		2,451
OTTI (gain) loss included in AOCI	0	[1]	0	[2]
Corporate debt securities
Securities available-for-sale
Total fixed maturities	12,388,886	[3]	11,258,517	[4]
Gross unrealized gains	437,207	[3]	763,036	[4]
Gross unrealized losses	320,381	[3]	82,104	[4]
Fixed maturities, available-for-sale	12,505,712	[3]	11,939,449	[4]
OTTI (gain) loss included in AOCI	(1,810)	[1],[3]	(2,228)	[2],[4]
Perpetual debt investments
Securities available-for-sale
Total fixed maturities	149,062		157,742
Fixed maturities, available-for-sale	116,423		131,799
Asset-backed securities
Securities available-for-sale
Total fixed maturities	1,196,326		1,263,089
Gross unrealized gains	128,406		149,152
Gross unrealized losses	13,362		13,702
Fixed maturities, available-for-sale	1,311,370		1,398,539
OTTI (gain) loss included in AOCI	(86,474)	[1]	(96,603)	[2]
Residential mortgage-backed securities
Securities available-for-sale
Total fixed maturities	122,146		167,793
Gross unrealized gains	4,734		7,368
Gross unrealized losses	1,508		1,932
Fixed maturities, available-for-sale	125,372		173,229
OTTI (gain) loss included in AOCI	(123)	[1]	(185)	[2]
Commercial mortgage-backed securities
Securities available-for-sale
Total fixed maturities	1,009,320		886,748
Gross unrealized gains	19,117		32,556
Gross unrealized losses	11,529		1,099
Fixed maturities, available-for-sale	1,016,908		918,205
OTTI (gain) loss included in AOCI	0	[1]	0	[2]
Collateralized debt obligations
Securities available-for-sale
Total fixed maturities	9,112		10,674
Gross unrealized gains	0		0
Gross unrealized losses	58		209
Fixed maturities, available-for-sale	9,054		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 $149,062 and estimated fair value of $116,423.

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