Derivative Instruments (Detail) - Gross amounts of derivative fair values contained in the consolidated balance sheet (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011		Dec. 31, 2010
Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Total derivatives as hedging instruments	$ 192,643	[1]	$ 117,594	[1]
Total derivatives as hedging instruments	(1,368)	[1]	(12,161)	[1]
Designated as Hedging Instrument [Member] | Other Assets, Notional [Member]
Derivatives designated as hedging instruments:
Total derivatives as hedging instruments	2,685,820		2,011,120
Designated as Hedging Instrument [Member] | Other Liabilities, Notional [Member]
Derivatives designated as hedging instruments:
Total derivatives as hedging instruments	41,630		244,731
Other Assets, Notional [Member] | Investment Related Derivatives [Member]
Derivatives not designated as hedging instruments:
Interest rate exposure	104,614		117,689
Foreign exchange exposure	95,626		82,395
Credit exposure	212,500		128,450
Financial market exposure	121,107		135,912
Commodity futures	4,456
Other Assets, Notional [Member] | Financial Operations Derivatives [Member]
Derivatives not designated as hedging instruments:
Credit exposure		[2],[3]		[2],[3]
Other Assets, Notional [Member] | Other Non-Investment Derivatives [Member]
Derivatives not designated as hedging instruments:
Contingent capital facility	350,000		350,000
Other Assets, Notional [Member] | Not Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Total derivatives as hedging instruments	888,303		814,446
Other Assets, Notional [Member] | Interest Rate Contract [Member]
Derivatives designated as hedging instruments:
Interest rate contracts (2)	159,056	[2]	161,028	[2]
Other Assets, Notional [Member] | Foreign Exchange Contract [Member]
Derivatives designated as hedging instruments:
Foreign exchange contracts	2,526,764		1,850,092
Other Liabilities, Notional [Member] | Investment Related Derivatives [Member]
Derivatives not designated as hedging instruments:
Interest rate exposure	4,128		41,063
Foreign exchange exposure	372,456		272,724
Credit exposure	419,513		532,000
Financial market exposure	22,668		4,575
Other Liabilities, Notional [Member] | Financial Operations Derivatives [Member]
Derivatives not designated as hedging instruments:
Credit exposure	174,936	[2],[3]	246,292	[2],[3]
Other Liabilities, Notional [Member] | Other Non-Investment Derivatives [Member]
Derivatives not designated as hedging instruments:
Guaranteed minimum income benefit contract	83,957		80,025
Modified coinsurance funds withheld contract	69,175		72,509
Other Liabilities, Notional [Member] | Not Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Total derivatives as hedging instruments	1,146,833		1,249,188
Other Liabilities, Notional [Member] | Interest Rate Contract [Member]
Derivatives designated as hedging instruments:
Interest rate contracts (2)		[2]		[2]
Other Liabilities, Notional [Member] | Foreign Exchange Contract [Member]
Derivatives designated as hedging instruments:
Foreign exchange contracts	41,630		244,731
Investment Related Derivatives [Member]
Derivatives not designated as hedging instruments:
Interest rate exposure	1,390	[1]	281	[1]
Interest rate exposure	(49)	[1]		[1]
Foreign exchange exposure	3,023	[1]	1,377	[1]
Foreign exchange exposure	(14,254)	[1]	(6,329)	[1]
Credit exposure	6,004	[1]	8,143	[1]
Credit exposure	(7,847)	[1]	(5,295)	[1]
Financial market exposure	653	[1]	705	[1]
Financial market exposure	(2,334)	[1]	(27)	[1]
Financial Operations Derivatives [Member]
Derivatives not designated as hedging instruments:
Credit exposure		[1],[2],[3]		[1],[2],[3]
Credit exposure	(25,887)	[1],[2],[3]	(25,887)	[1],[2],[3]
Other Non-Investment Derivatives [Member]
Derivatives not designated as hedging instruments:
Contingent capital facility		[1]
Contingent capital facility		[1]
Guaranteed minimum income benefit contract		[1]		[1]
Guaranteed minimum income benefit contract	(22,050)	[1]	(21,190)	[1]
Modified coinsurance funds withheld contract		[1]
Modified coinsurance funds withheld contract		[1]
Not Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Total derivatives as hedging instruments	11,070	[1]	10,506	[1]
Total derivatives as hedging instruments	(72,421)	[1]	(58,728)	[1]
Interest Rate Contract [Member]
Derivatives designated as hedging instruments:
Interest rate contracts (2)	107,707	[1],[2]	74,368	[1],[2]
Interest rate contracts (2)		[1],[2]		[1],[2]
Foreign Exchange Contract [Member]
Derivatives designated as hedging instruments:
Foreign exchange contracts	84,936	[1]	43,226	[1]
Foreign exchange contracts	$ (1,368)	[1]	$ (12,161)	[1]

[1] Derivative instruments in an asset or liability position are included within Other Assets or Other Liabilities, respectively, in the consolidated balance sheet.

[2] At September 30, 2011 and December 31, 2010, the Company held net cash collateral related to these derivative positions of $54.0 million and $23.0 million, respectively. The collateral balance is included within cash and cash equivalents and the corresponding liability to return the collateral has been offset against the derivative positions within the balance sheet as appropriate under the netting agreement.

[3] Financial operations derivatives represent interests in variable interest entities as described in Note 11, "Variable Interest Entities."