Business Segments (Balance Sheet Information) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 4,768us-gaap_ReinsuranceRecoverablesGross	$ 4,742us-gaap_ReinsuranceRecoverablesGross
Insurance receivables	2,109us-gaap_PremiumsReceivableGross	1,997us-gaap_PremiumsReceivableGross
Deferred acquisition costs	616us-gaap_DeferredPolicyAcquisitionCosts	600us-gaap_DeferredPolicyAcquisitionCosts
Goodwill	151us-gaap_Goodwill	152us-gaap_Goodwill
Insurance reserves
Claim and claim adjustment expenses	23,248	23,271
Unearned premiums	3,710us-gaap_UnearnedPremiums	3,592us-gaap_UnearnedPremiums
Future policy benefits	9,747	9,490
Policyholders’ funds	0us-gaap_PolicyholderContractDeposits	27us-gaap_PolicyholderContractDeposits
Specialty [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	671	567
Insurance receivables	808	778
Deferred acquisition costs	307	304
Goodwill	117	117
Insurance reserves
Claim and claim adjustment expenses	6,352	6,229
Unearned premiums	1,794	1,763
Future policy benefits	0	0
Policyholders’ funds		9
Commercial [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	675	690
Insurance receivables	1,004	954
Deferred acquisition costs	225	213
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	9,441	9,514
Unearned premiums	1,329	1,273
Future policy benefits	0	0
Policyholders’ funds		18
International [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	207	207
Insurance receivables	282	250
Deferred acquisition costs	84	83
Goodwill	34	35
Insurance reserves
Claim and claim adjustment expenses	1,377	1,441
Unearned premiums	449	431
Future policy benefits	0	0
Policyholders’ funds		0
Life and Group Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	543	525
Insurance receivables	13	13
Deferred acquisition costs	0	0
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	3,237	3,183
Unearned premiums	139	125
Future policy benefits	9,747	9,490
Policyholders’ funds		0
Corporate and Other Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	2,672	2,753
Insurance receivables	2	2
Deferred acquisition costs	0	0
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	2,841	2,904
Unearned premiums	0	0
Future policy benefits	0	0
Policyholders’ funds		0
Eliminations [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	0	0
Insurance receivables	0	0
Deferred acquisition costs	0	0
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	0	0
Unearned premiums	(1)	0
Future policy benefits	0	0
Policyholders’ funds		$ 0

Net amount of deferred policy acquisition costs capitalized on contracts remaining in force as of the balance sheet date.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 16

-Article 12

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 825

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6487548&loc=d3e32546-158582

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 30

-Section 55

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35755678&loc=d3e11446-158418

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 30

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6481648&loc=d3e11198-158413

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.(a),7)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Article 7

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- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

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-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

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- Details

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- Definition

The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 3

-Subparagraph (a),(b),(c)

-URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437

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- Definition

Amount of accrued obligation to policyholders that relates to insured events for long-duration contracts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 25

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=28366191&loc=d3e13145-158430

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 13

-Subparagraph a

-Article 7

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.13(a)(1))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

The liability as of the balance sheet date to the policyholders for deposits held under the terms of insurance contracts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.13(a)(3))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

-Publisher FASB

-Name Accounting Standards Codification

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-Section 30

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-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=28366349&loc=d3e13951-158433

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- Definition

Gross amount, as of the balance sheet date, due the entity from (a) agents and insureds, (b) uncollected premiums and (c) others, before deducting the allowance for doubtful accounts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.5)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 5

-Article 7

+ Details

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Balance Type:	debit
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- Definition

Amount before valuation allowance recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

+ References

No definition available.

+ Details

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- Definition

Carrying amount of premiums written on insurance contracts that have not been earned as of the balance sheet date.

+ References

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