Fair Value Measurements (details) - Changes in Level 3 (USD $) In Millions	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2011	Sep. 30, 2011	Dec. 31, 2010
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	$ 268	$ 287	$ 394
Level 3 fair value category, total realized and unrealized investment gains (losses) included in realized investment gains (losses)	34	40	7
Level 3 fair value category, total realized and unrealized investment gains (losses) included in increases (decreases) in accumulated other chages in equity from nonowner sources	(25)	(12)	21
Level 3 fair value category purchases	40	124	47
Level 3 fair value category sales	(43)	(62)	(122)
Level 3 fair value category settlements/maturities	(5)	(26)	(41)
Gross transfers into Level 3	8	16	13
Gross transfers out of Level 3		(90)	(32)
Level 3 fair value category, ending balance	277	277	287
Fixed maturities [Member]
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	197	230	240
Level 3 fair value category, total realized and unrealized investment gains (losses) included in realized investment gains (losses)	1	1	5
Level 3 fair value category, total realized and unrealized investment gains (losses) included in increases (decreases) in accumulated other chages in equity from nonowner sources	(3)	(3)	10
Level 3 fair value category purchases	37	119	44
Level 3 fair value category sales	(3)	(15)	(9)
Level 3 fair value category settlements/maturities	(5)	(26)	(41)
Gross transfers into Level 3	8	16	13
Gross transfers out of Level 3		(90)	(32)
Level 3 fair value category, ending balance	232	232	230
Other investments [Member]
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	71	57	154
Level 3 fair value category, total realized and unrealized investment gains (losses) included in realized investment gains (losses)	33	39	2
Level 3 fair value category, total realized and unrealized investment gains (losses) included in increases (decreases) in accumulated other chages in equity from nonowner sources	(22)	(9)	11
Level 3 fair value category purchases	3	5	3
Level 3 fair value category sales	(40)	(47)	(113)
Level 3 fair value category, ending balance	$ 45	$ 45	$ 57

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Name Accounting Standards Codification

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- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in other comprehensive income (a separate component of shareholders' equity).

+ References

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- Definition

Purchases that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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- Definition

Sales that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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Settlements that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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- Definition

Transfers into assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

+ References

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-Name Accounting Standards Codification

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Transfers out of assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

+ References

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-Name Accounting Standards Codification

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- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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