Fair Value Measurements (details) - Changes in Level 3 (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended	12 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2012	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Fixed maturities [Member]	Jun. 30, 2012 Fixed maturities [Member]	Dec. 31, 2011 Fixed maturities [Member]	Jun. 30, 2012 Other investments [Member]	Dec. 31, 2011 Other investments [Member]	Mar. 31, 2012 Other investments [Member]
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	$ 294	$ 294	$ 287	$ 250	$ 250	$ 230	$ 44	$ 57	$ 44
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in realized investment gains (losses)	1	1	39	1	2	1	(1)	38
Level 3 fair value category, total unrealized investment gains (losses) reported in increases (decreases) in other comprehensive income		5	(9)		4		1	(9)
Level 3 fair value category purchases	33	50	159	33	50	154		5
Level 3 fair value category sales			(62)			(15)		(47)
Level 3 fair value category settlements/maturities	(25)	(45)	(43)	(25)	(45)	(43)
Gross transfers into Level 3	6	6	19	6	6	19
Gross transfers out of Level 3	(11)	(13)	(96)	(11)	(13)	(96)
Level 3 fair value category, ending balance	$ 298	$ 298	$ 294	$ 254	$ 254	$ 250	$ 44	$ 44	$ 44

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Amount of gain (loss) recognized in earnings, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

+ References

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- Definition

Amount of gain (loss) recognized in other comprehensive income, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

+ 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

+ Details

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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.

+ References

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- Definition

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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- Definition

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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- 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 Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Reference 2: 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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