Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Consolidated Variable Interest Entity Gains (Losses) [Line Items]
Number of CLN structures invested in and consolidated by the company	2
Percent of outstanding notes of the CLN structures invested in by the company and third parties	100.00%
Credit Linked Notes By Industry And Ratings [Line Items]
Telecommunications	11.20%
Financial intermediaries	10.50%
Oil and gas	6.30%
Utilities	4.50%
Chemicals and plastics	3.90%
Drugs	3.70%
Retailers (except food and drug)	3.50%
Industrial equipment	3.30%
Sovereign	3.30%
Food products	3.20%
Conglomerates	3.10%
Forest products	3.00%
Other	40.50%
Total by Industry	100.00%
Unconsolidated VIE long term senior note	$ 500
Excess mortality swap note	100
External Credit Rating AAA [Member]
Credit Linked Notes By Industry And Ratings [Line Items]
Telecommunications	0.00%
Financial intermediaries	0.30%
Oil and gas	0.00%
Utilities	0.00%
Chemicals and plastics	0.00%
Drugs	0.30%
Retailers (except food and drug)	0.00%
Industrial equipment	0.00%
Sovereign	0.00%
Food products	0.00%
Conglomerates	0.00%
Forest products	0.00%
Other	0.00%
Total by Industry	0.60%
External Credit Rating AA [Member]
Credit Linked Notes By Industry And Ratings [Line Items]
Telecommunications	0.00%
Financial intermediaries	3.30%
Oil and gas	0.70%
Utilities	0.00%
Chemicals and plastics	0.00%
Drugs	2.20%
Retailers (except food and drug)	0.00%
Industrial equipment	0.00%
Sovereign	0.70%
Food products	0.30%
Conglomerates	2.60%
Forest products	0.00%
Other	3.00%
Total by Industry	12.80%
External Credit Rating A [Member]
Credit Linked Notes By Industry And Ratings [Line Items]
Telecommunications	5.50%
Financial intermediaries	6.40%
Oil and gas	1.00%
Utilities	3.10%
Chemicals and plastics	2.30%
Drugs	1.20%
Retailers (except food and drug)	2.10%
Industrial equipment	3.00%
Sovereign	1.60%
Food products	1.80%
Conglomerates	0.50%
Forest products	0.00%
Other	14.90%
Total by Industry	43.40%
External Credit Rating BBB [Member]
Credit Linked Notes By Industry And Ratings [Line Items]
Telecommunications	4.80%
Financial intermediaries	0.50%
Oil and gas	4.60%
Utilities	1.40%
Chemicals and plastics	1.20%
Drugs	0.00%
Retailers (except food and drug)	0.90%
Industrial equipment	0.30%
Sovereign	1.00%
Food products	1.10%
Conglomerates	0.00%
Forest products	1.60%
Other	17.30%
Total by Industry	34.70%
External Credit Rating BB [Member]
Credit Linked Notes By Industry And Ratings [Line Items]
Telecommunications	0.40%
Financial intermediaries	0.00%
Oil and gas	0.00%
Utilities	0.00%
Chemicals and plastics	0.40%
Drugs	0.00%
Retailers (except food and drug)	0.50%
Industrial equipment	0.00%
Sovereign	0.00%
Food products	0.00%
Conglomerates	0.00%
Forest products	1.40%
Other	3.50%
Total by Industry	6.20%
External Credit Rating B [Member]
Credit Linked Notes By Industry And Ratings [Line Items]
Telecommunications	0.50%
Financial intermediaries	0.00%
Oil and gas	0.00%
Utilities	0.00%
Chemicals and plastics	0.00%
Drugs	0.00%
Retailers (except food and drug)	0.00%
Industrial equipment	0.00%
Sovereign	0.00%
Food products	0.00%
Conglomerates	0.00%
Forest products	0.00%
Other	1.50%
Total by Industry	2.00%
External Credit Rating CCC [Member]
Credit Linked Notes By Industry And Ratings [Line Items]
Telecommunications	0.00%
Financial intermediaries	0.00%
Oil and gas	0.00%
Utilities	0.00%
Chemicals and plastics	0.00%
Drugs	0.00%
Retailers (except food and drug)	0.00%
Industrial equipment	0.00%
Sovereign	0.00%
Food products	0.00%
Conglomerates	0.00%
Forest products	0.00%
Other	0.30%
Total by Industry	0.30%
Credit Linked Note Structure December 2006 [Member]
Credit Linked Notes Structures Summary Information [Line Items]
Amount of Issuance	400
Date of Issuance	December 2006
Original attachment point (subordination)	5.50%
Current attachment point (subordination)	4.17%
Maturity	12/20/2016
Current rating of tranche	B+
Current rating of underlying collateral pool, high end of range	Aa1
Current rating of underlying collateral pool, low end of range	B3
Number of defaults in underlying collateral pool	2
Number of entities	123
Number of countries	19
Credit Linked Note Structure April 2007 [Member]
Credit Linked Notes Structures Summary Information [Line Items]
Amount of Issuance	200
Date of Issuance	April 2007
Original attachment point (subordination)	2.05%
Current attachment point (subordination)	1.48%
Maturity	3/20/2017
Current rating of tranche	Ba2
Current rating of underlying collateral pool, high end of range	Aaa
Current rating of underlying collateral pool, low end of range	Caa1
Number of defaults in underlying collateral pool	2
Number of entities	99
Number of countries	22
Derivative Instruments Not Designated and Not Qualifying as Hedging Instruments
Consolidated Variable Interest Entity Gains (Losses) [Line Items]
Gains (losses) for consolidated variable interest entities	(82)	16
Derivative Instruments Not Designated and Not Qualifying as Hedging Instruments | Credit default swaps [Member]
Consolidated Variable Interest Entity Gains (Losses) [Line Items]
Gains (losses) for consolidated variable interest entities	(80)	25
Derivative Instruments Not Designated and Not Qualifying as Hedging Instruments | Contingent Forwards [Member]
Consolidated Variable Interest Entity Gains (Losses) [Line Items]
Gains (losses) for consolidated variable interest entities	(2)	(9)
Assets
Consolidated Variable Interest Entity Asset and Liability information [Line Items]
Number of Instruments	1	0
Notional Amounts	100	0
Carrying Value	700	584
Assets | Fixed maturity corporate asset-backed credit card loan securities [Member]
Consolidated Variable Interest Entity Asset and Liability information [Line Items]
Notional Amounts	0	0
Carrying Value	592	584
Assets | U.S. government bonds [Member]
Consolidated Variable Interest Entity Asset and Liability information [Line Items]
Notional Amounts	0	0
Carrying Value	108	0
Assets | Excess mortality swap [Member]
Consolidated Variable Interest Entity Asset and Liability information [Line Items]
Number of Instruments	1	0
Notional Amounts	100	0
Carrying Value	0	0
Liabilities
Consolidated Variable Interest Entity Asset and Liability information [Line Items]
Number of Instruments	4	4
Notional Amounts	600	600
Carrying Value	193	132
Liabilities | Derivative Instruments Not Designated and Not Qualifying as Hedging Instruments
Consolidated Variable Interest Entity Asset and Liability information [Line Items]
Number of Instruments	4	4
Notional Amounts	600	600
Carrying Value	291	209
Liabilities | Credit default swaps [Member] | Derivative Instruments Not Designated and Not Qualifying as Hedging Instruments
Consolidated Variable Interest Entity Asset and Liability information [Line Items]
Number of Instruments	2	2
Notional Amounts	600	600
Carrying Value	295	215
Liabilities | Contingent Forwards [Member] | Derivative Instruments Not Designated and Not Qualifying as Hedging Instruments
Consolidated Variable Interest Entity Asset and Liability information [Line Items]
Number of Instruments	2	2
Notional Amounts	0	0
Carrying Value	(4)	(6)
Liabilities | Federal Income Tax Liability [Member]
Consolidated Variable Interest Entity Asset and Liability information [Line Items]
Notional Amounts	0	0
Carrying Value	$ (98)	$ (77)