Business Segments (Balance Sheet Information) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 4,539	$ 4,742
Insurance receivables	2,111	1,997
Deferred acquisition costs	606	600
Goodwill	151	152
Insurance reserves
Claim and claim adjustment expenses	22,867	23,271
Unearned premiums	3,706	3,592
Future policy benefits	9,520	9,490
Policyholders’ funds	0	27
Specialty [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	619	567
Insurance receivables	851	778
Deferred acquisition costs	305	304
Goodwill	117	117
Insurance reserves
Claim and claim adjustment expenses	6,199	6,229
Unearned premiums	1,817	1,763
Future policy benefits	0	0
Policyholders’ funds		9
Commercial [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	664	690
Insurance receivables	996	954
Deferred acquisition costs	216	213
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	9,283	9,514
Unearned premiums	1,307	1,273
Future policy benefits	0	0
Policyholders’ funds		18
International [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	172	207
Insurance receivables	252	250
Deferred acquisition costs	85	83
Goodwill	34	35
Insurance reserves
Claim and claim adjustment expenses	1,365	1,441
Unearned premiums	455	431
Future policy benefits	0	0
Policyholders’ funds		0
Life and Group Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	517	525
Insurance receivables	10	13
Deferred acquisition costs	0	0
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	3,286	3,183
Unearned premiums	127	125
Future policy benefits	9,520	9,490
Policyholders’ funds		0
Corporate and Other Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	2,567	2,753
Insurance receivables	2	2
Deferred acquisition costs	0	0
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	2,734	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	0	0
Future policy benefits	$ 0	0
Policyholders’ funds		$ 0