Reinsurance (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts, life insurance in force	$ 88,045us-gaap_LifeInsuranceInForceGross	$ 85,015us-gaap_LifeInsuranceInForceGross	$ 81,467us-gaap_LifeInsuranceInForceGross
Gross amounts	4,468us-gaap_DirectPremiumsEarned	4,151us-gaap_DirectPremiumsEarned	3,755us-gaap_DirectPremiumsEarned
Ceded amounts to other companies, life insurance in force	37,689us-gaap_LifeInsuranceInForceCeded	36,952us-gaap_LifeInsuranceInForceCeded	36,340us-gaap_LifeInsuranceInForceCeded
Ceded amounts to other companies	237us-gaap_CededPremiumsEarned	260us-gaap_CededPremiumsEarned	242us-gaap_CededPremiumsEarned
Assumed amounts from other companies, life insurance in force	0us-gaap_LifeInsuranceInForceAssumed	0us-gaap_LifeInsuranceInForceAssumed	0us-gaap_LifeInsuranceInForceAssumed
Assumed amounts from other companies	12us-gaap_AssumedPremiumsEarned	11us-gaap_AssumedPremiumsEarned	9us-gaap_AssumedPremiumsEarned
Net amounts, life insurance in force	50,356us-gaap_LifeInsuranceInForceNet	48,063us-gaap_LifeInsuranceInForceNet	45,126us-gaap_LifeInsuranceInForceNet
Premiums Earned, Net	4,243us-gaap_PremiumsEarnedNet	3,902us-gaap_PremiumsEarnedNet	3,522us-gaap_PremiumsEarnedNet
Percentage of amounts assumed to net, life insurance in force	0.00%	0.00%	0.00%
Percentage of amounts assumed to net	0.50%us-gaap_PremiumsPercentageAssumedToNet	0.50%us-gaap_PremiumsPercentageAssumedToNet	0.30%us-gaap_PremiumsPercentageAssumedToNet
Commercial Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts	2,973	2,777	2,524
Ceded amounts to other companies	128	151	149
Assumed amounts from other companies	11	10	8
Premiums Earned, Net	2,856	2,636	2,383
Percentage of amounts assumed to net	0.40%	0.40%	0.30%
Personal Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts	1,080	1,002	897
Ceded amounts to other companies	40	42	30
Assumed amounts from other companies	1	1	1
Premiums Earned, Net	1,041	961	868
Percentage of amounts assumed to net	0.10%	0.10%	0.10%
Excess And Surplus Lines Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts	156	124	99
Ceded amounts to other companies	8	8	6
Assumed amounts from other companies	0	0	0
Premiums Earned, Net	148	116	93
Percentage of amounts assumed to net	0.00%	0.00%	0.00%
Property, Liability And Casualty Insurance Segment [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts	4,209	3,903	3,520
Ceded amounts to other companies	176	201	185
Assumed amounts from other companies	12	11	9
Premiums Earned, Net	4,045	3,713	3,344
Percentage of amounts assumed to net	0.50%	0.50%	0.30%
Life Insurance Segment
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts	259	248	235
Ceded amounts to other companies	61	59	57
Assumed amounts from other companies	0	0	0
Premiums Earned, Net	$ 198	$ 189	$ 178
Percentage of amounts assumed to net	0.00%	0.00%	0.00%

Amount of earned premiums assumed from other entities.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 17

-Article 12

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 235

-Section S99

-Paragraph 2

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-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.1)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 605

-Section 50

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-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

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

-Publisher SEC

-Name Regulation S-X (SX)

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Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 17

-Article 12

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 235

-Section S99

-Paragraph 2

-Subparagraph (SX 210.12-17)

-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.1)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 1

-Article 7

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

-Publisher FASB

-Name Accounting Standards Codification

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-Section 50

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Amount of life insurance issued and outstanding assumed from other entities. Includes, but not limited to, dividends and adjustments to face value.

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Amount of life insurance issued and outstanding ceded to other entities. Includes, but not limited to, dividends and adjustments to face value.

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Amount before contracts ceded to other entities and contracts assumed by the entity of life insurance issued and outstanding. Includes, but not limited to, dividends and adjustments to face value.

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Amount after contracts ceded to other entities and contracts assumed by the entity of life insurance issued and outstanding. Includes, but not limited to, dividends and adjustments to face value.

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Percentage of assumed life insurance issued and outstanding contracts to life insurance issued and outstanding after contracts ceded to other entities and contracts assumed by the entity. Includes, but not limited to, dividends and adjustments to face value.

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Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 17

-Article 12

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 235

-Section S99

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-Subparagraph (SX 210.12-17)

-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.1)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 1

-Article 7

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 605

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

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

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-Name Accounting Standards Codification

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