Business Segments (Balance Sheet Information) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 4,702	$ 4,742
Insurance receivables	2,245	1,997
Deferred acquisition costs	621	600
Goodwill	153	152
Insurance reserves
Claim and claim adjustment expenses	23,193	23,271
Unearned premiums	3,815	3,592
Future policy benefits	9,360	9,490
Policyholders’ funds	0	27
Specialty [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	697	567
Insurance receivables	862	778
Deferred acquisition costs	306	304
Goodwill	117	117
Insurance reserves
Claim and claim adjustment expenses	6,365	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	660	690
Insurance receivables	1,068	954
Deferred acquisition costs	224	213
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	9,391	9,514
Unearned premiums	1,384	1,273
Future policy benefits	0	0
Policyholders’ funds		18
International [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	192	207
Insurance receivables	302	250
Deferred acquisition costs	91	83
Goodwill	36	35
Insurance reserves
Claim and claim adjustment expenses	1,401	1,441
Unearned premiums	506	431
Future policy benefits	0	0
Policyholders’ funds		0
Life and Group Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	534	525
Insurance receivables	10	13
Deferred acquisition costs	0	0
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	3,248	3,183
Unearned premiums	132	125
Future policy benefits	9,360	9,490
Policyholders’ funds		0
Corporate and Other Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	2,619	2,753
Insurance receivables	3	2
Deferred acquisition costs	0	0
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	2,788	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