Investments (Details) - Narrative (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012 positions	Jun. 30, 2011	Jun. 30, 2012 positions	Jun. 30, 2011	Dec. 31, 2011
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	$ 26,242,802,000		$ 26,242,802,000		$ 26,190,025,000
Cost or Amortized cost of Fixed maturities	25,442,779,000		25,442,779,000		25,771,715,000
Fixed maturities, held to maturity	2,716,357,000		2,716,357,000		2,668,978,000
Held To Maturity Securities Fair Value	3,006,992,000		3,006,992,000		2,895,688,000
Fair value of securities - AFS	26,999,238,000		26,999,238,000		27,017,285,000
Available-for-sale Securities, Amortized Cost Basis	26,223,815,000		26,223,815,000		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	34.20%		34.20%		31.40%
Percentage of HTM securities rated A or higher	97.30%		97.30%
Unrealized appreciation related to securities reclassified from AFS to HTM			131,500,000
Unamortized portion of appreciation related to securities reclassified	105,500,000		105,500,000		108,400,000
Pledged assets, amount	17,500,000,000		17,500,000,000		17,200,000,000
Unrealized losses on AFS portfolio	576,800,000		576,800,000
Total number of positions - AFS	7,156		7,156
AFS securities in unrealized loss position (number of positions)	1,308		1,308
Unrealized losses on HTM portfolio	12,500,000		12,500,000
Total number of positions - HTM	208		208
HTM securities in unrealized loss position (number of positions)	15		15
OTTI on investments, net of amounts transferred to other comprehensive income	28,193,000	27,176,000	49,158,000	64,621,000
Credit loss impairments previously recognized on securities which matured, paid down, prepaid or were sold during the period	40,797,000	38,316,000	59,737,000	164,027,000
Maximum
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Short term investments maturity horizon from reporting date			1 year
P&C
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Unrealized loss			55,200,000
Government Related Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Total fair value	2,066,000,000		2,066,000,000		1,915,600,000
Total cost or amortized cost	2,012,400,000		2,012,400,000		1,878,300,000
U.S. Agency Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Total fair value	500,500,000		500,500,000		541,200,000
Total cost or amortized cost	455,000,000		455,000,000		494,000,000
Other asset-backed securities
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	1,407,738,000		1,407,738,000		1,340,249,000
Cost or Amortized cost of Fixed maturities	1,392,065,000		1,392,065,000		1,341,309,000
Fixed maturities, held to maturity	217,347,000		217,347,000		288,741,000
Held To Maturity Securities Fair Value	237,039,000		237,039,000		309,296,000
Covered Bonds [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	500,500,000		500,500,000		353,900,000
Cost or Amortized cost of Fixed maturities	478,100,000		478,100,000		345,400,000
Fixed maturities, held to maturity	8,100,000		8,100,000		8,100,000
Held To Maturity Securities Fair Value	7,800,000		7,800,000		7,700,000
Unrealized losses on HTM portfolio	8,100,000		8,100,000		7,700,000
Corporate
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	9,721,153,000		9,721,153,000		10,108,622,000
Cost or Amortized cost of Fixed maturities	9,297,657,000		9,297,657,000		9,866,677,000
Fixed maturities, held to maturity	1,387,033,000		1,387,033,000		1,290,209,000
Held To Maturity Securities Fair Value	1,509,453,000		1,509,453,000		1,367,089,000
OTTI on investments, net of amounts transferred to other comprehensive income			2,200,000
Medium-term Notes [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	186,100,000		186,100,000		266,000,000
Cost or Amortized cost of Fixed maturities	199,100,000		199,100,000		297,700,000
OTTI on investments, net of amounts transferred to other comprehensive income			10,200,000
Medium-term Notes [Member] | P&C
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Unrealized loss			14,300,000
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	346,200,000		346,200,000		386,100,000
Cost or Amortized cost of Fixed maturities	420,300,000		420,300,000		494,900,000
Unrealized losses on AFS portfolio	74,700,000		74,700,000		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	34,300,000		34,300,000		44,700,000
Equity Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income			1,500,000
Fixed Income Funds Member
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fair value of securities - AFS	95,800,000		95,800,000		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	26,300,000		26,300,000
Cumulative fair value decline (as a percentage of amortized cost)			50.00%
OTTI on investments, net of amounts transferred to other comprehensive income			14,300,000
Structured Credit Securities [Member] | Change in intent
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income			0
Change of intent from sell to hold (number of positions)			0
RMBS - Non-Agency
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	584,543,000		584,543,000		641,815,000
Cost or Amortized cost of Fixed maturities	728,309,000		728,309,000		851,557,000
Fixed maturities, held to maturity	81,028,000		81,028,000		80,955,000
Held To Maturity Securities Fair Value	87,090,000		87,090,000		87,443,000
Credit loss impairments previously recognized on securities which matured, paid down, prepaid or were sold during the period	21,900,000	20,900,000	31,800,000	112,600,000
RMBS - Non-Agency | AFS
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Unrealized loss			32,700,000
CMBS
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Fixed maturities, at fair value	904,792,000		904,792,000		974,835,000
Cost or Amortized cost of Fixed maturities	842,802,000		842,802,000		927,684,000
Fixed maturities, held to maturity	12,546,000		12,546,000
Held To Maturity Securities Fair Value	14,213,000		14,213,000
Unrealized loss			800,000
Core CDO
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Unrealized loss			$ 21,700,000