Investments (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Available for sale fixed maturities and equity securities
Gross Unrealized, Losses	$ (52)
U.S. Government and government agencies [Member]
Available for sale fixed maturities and equity securities
Amortized Cost	327	373
Fair Value	342	388
Gross Unrealized, Gains	15	15
Gross Unrealized, Losses
States, municipalities and political subdivisions [Member]
Available for sale fixed maturities and equity securities
Amortized Cost	4,334	4,144
Fair Value	4,644	4,468
Gross Unrealized, Gains	316	329
Gross Unrealized, Losses	(6)	(5)
Foreign government [Member]
Available for sale fixed maturities and equity securities
Amortized Cost	238	242
Fair Value	254	260
Gross Unrealized, Gains	16	18
Residential Mortgage Backed Securities [Member]
Available for sale fixed maturities and equity securities
Amortized Cost	3,922	3,921
Fair Value	4,262	4,204
Gross Unrealized, Gains	378	337
Gross Unrealized, Losses	(38)	(54)
Commercial Mortgage Backed Securities [Member]
Available for sale fixed maturities and equity securities
Amortized Cost	2,556	2,583
Fair Value	2,859	2,918
Gross Unrealized, Gains	303	335
Gross Unrealized, Losses		0
Asset-backed Securities [Member]
Available for sale fixed maturities and equity securities
Amortized Cost	1,954	1,590
Fair Value	2,014	1,640
Gross Unrealized, Gains	62	52
Gross Unrealized, Losses	(2)	(2)
All other corporate [Member]
Available for sale fixed maturities and equity securities
Amortized Cost	9,424	9,230
Fair Value	10,400	10,240
Gross Unrealized, Gains	982	1,015
Gross Unrealized, Losses	(6)	(5)
Fixed maturities [Member]
Available for sale fixed maturities and equity securities
Amortized Cost	22,755	22,083
Fair Value	24,775	24,118
Gross Unrealized, Gains	2,072	2,101
Gross Unrealized, Losses	(52)	(66)
Common stocks [Member]
Available for sale fixed maturities and equity securities
Amortized Cost	655	600
Fair Value	867	749
Gross Unrealized, Gains	215	157
Gross Unrealized, Losses	(3)	(8)
Perpetual preferred stocks [Member]
Available for sale fixed maturities and equity securities
Amortized Cost	182	178
Fair Value	198	190
Gross Unrealized, Gains	17	13
Gross Unrealized, Losses	$ (1)	$ (1)

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

-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.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-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.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-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.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

-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.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15E

-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.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-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.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-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.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

-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.

+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details