Investments (Details) - Narrative (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012 positions	Sep. 30, 2011	Sep. 30, 2012 positions	Sep. 30, 2011	Dec. 31, 2011
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	$ 27,426,293,000		$ 27,426,293,000		$ 26,190,025,000
Cost or Amortized cost of Fixed maturities	26,150,520,000		26,150,520,000		25,771,715,000
Fixed maturities, held to maturity	2,805,796,000		2,805,796,000		2,668,978,000
Held To Maturity Securities Fair Value	3,222,900,000		3,222,900,000		2,895,688,000
Fair value of securities - AFS	28,315,925,000		28,315,925,000		27,017,285,000
Available-for-sale Securities, Amortized Cost Basis	27,028,521,000		27,028,521,000		26,611,778,000
Percentage of fixed income portfolio invested in securities below investment grade	2.70%		2.70%		2.40%
Percentage of gross unrealized losses relating to securities below investment grade	36.20%		36.20%		31.40%
Percentage of HTM securities rated A or higher	96.50%		96.50%
Unrealized appreciation related to securities reclassified from AFS to HTM			131,500,000
Unamortized portion of appreciation related to securities reclassified	107,000,000		107,000,000		108,400,000
Pledged assets, amount	17,500,000,000		17,500,000,000		17,200,000,000
Unrealized losses on AFS portfolio	396,600,000		396,600,000
Total number of positions - AFS	7,215		7,215
AFS securities in unrealized loss position (number of positions)	1,072		1,072
Unrealized losses on HTM portfolio	6,000,000		6,000,000
Total number of positions - HTM	207		207
HTM securities in unrealized loss position (number of positions)	9		9
OTTI on investments, net of amounts transferred to other comprehensive income	12,629,000	66,815,000	61,787,000	131,436,000
Credit loss impairments previously recognized on securities which matured, paid down, prepaid or were sold during the period	33,114,000	14,611,000	87,092,000	173,056,000
Maximum
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Short term investments maturity horizon from reporting date			1 year
Government Related Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Total fair value	2,258,600,000		2,258,600,000		1,915,600,000
Total cost or amortized cost	2,182,500,000		2,182,500,000		1,878,300,000
U.S. Agency Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Total fair value	499,500,000		499,500,000		541,200,000
Total cost or amortized cost	453,800,000		453,800,000		494,000,000
Other asset-backed securities
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	1,458,544,000		1,458,544,000		1,340,249,000
Cost or Amortized cost of Fixed maturities	1,421,005,000		1,421,005,000		1,341,309,000
Fixed maturities, held to maturity	224,508,000		224,508,000		288,741,000
Held To Maturity Securities Fair Value	253,431,000		253,431,000		309,296,000
Covered Bonds [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	599,900,000		599,900,000		353,900,000
Cost or Amortized cost of Fixed maturities	561,500,000		561,500,000		345,400,000
Fixed maturities, held to maturity	8,400,000		8,400,000		8,100,000
Held To Maturity Securities Fair Value	8,300,000		8,300,000		7,700,000
Unrealized losses on HTM portfolio	8,300,000		8,300,000		7,700,000
Corporate
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	10,007,137,000		10,007,137,000		10,108,622,000
Cost or Amortized cost of Fixed maturities	9,392,587,000		9,392,587,000		9,866,677,000
Fixed maturities, held to maturity	1,430,220,000		1,430,220,000		1,290,209,000
Held To Maturity Securities Fair Value	1,620,091,000		1,620,091,000		1,367,089,000
Medium-term Notes [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	192,300,000		192,300,000		266,000,000
Cost or Amortized cost of Fixed maturities	199,800,000		199,800,000		297,700,000
OTTI on investments, net of amounts transferred to other comprehensive income	2,200,000
Medium-term Notes [Member] | P&C
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Unrealized loss			10,200,000
Tier One and Upper Tier Two Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	348,800,000		348,800,000		386,100,000
Cost or Amortized cost of Fixed maturities	402,100,000		402,100,000		494,900,000
Unrealized losses on AFS portfolio	53,300,000		53,300,000		108,800,000
Covered bonds in fixed maturities and short-term investments [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Unrealized losses on AFS portfolio	599,900,000		599,900,000		353,900,000
Fixed Income Funds Member
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fair value of securities - AFS	99,300,000		99,300,000		91,600,000
Available-for-sale Securities, Amortized Cost Basis	100,000,000		100,000,000		100,000,000
Structured Credit Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Total fair value	12,000,000		12,000,000
OTTI on investments, net of amounts transferred to other comprehensive income	5,600,000
Structured Credit Securities [Member] | AFS
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Unrealized loss			37,000,000
RMBS - Non-Agency
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	636,325,000		636,325,000		641,815,000
Cost or Amortized cost of Fixed maturities	705,785,000		705,785,000		851,557,000
Fixed maturities, held to maturity	83,896,000		83,896,000		80,955,000
Held To Maturity Securities Fair Value	93,478,000		93,478,000		87,443,000
Credit loss impairments previously recognized on securities which matured, paid down, prepaid or were sold during the period	11,600,000	7,500,000	38,300,000	114,900,000
RMBS - Non-Agency | AFS
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Unrealized loss			21,600,000
CMBS
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	1,034,409,000		1,034,409,000		974,835,000
Cost or Amortized cost of Fixed maturities	963,365,000		963,365,000		927,684,000
Fixed maturities, held to maturity	12,917,000		12,917,000
Held To Maturity Securities Fair Value	15,026,000		15,026,000
Unrealized loss			600,000
Core CDO
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Unrealized loss			14,800,000
Private Investments [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income	$ 2,700,000