Business Segments (Balance Sheet Information) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 4,491	$ 4,742
Insurance receivables	2,129	1,997
Deferred acquisition costs	598	600
Goodwill	150	152
Insurance reserves
Claim and claim adjustment expenses	22,663	23,271
Unearned premiums	3,671	3,592
Future policy benefits	10,152	9,490
Policyholders’ funds	0	27
Specialty [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	724	567
Insurance receivables	890	778
Deferred acquisition costs	307	304
Goodwill	117	117
Insurance reserves
Claim and claim adjustment expenses	6,269	6,229
Unearned premiums	1,839	1,763
Future policy benefits	0	0
Policyholders’ funds		9
Commercial [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	639	690
Insurance receivables	993	954
Deferred acquisition costs	213	213
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	9,183	9,514
Unearned premiums	1,297	1,273
Future policy benefits	0	0
Policyholders’ funds		18
International [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	144	207
Insurance receivables	233	250
Deferred acquisition costs	78	83
Goodwill	33	35
Insurance reserves
Claim and claim adjustment expenses	1,347	1,441
Unearned premiums	415	431
Future policy benefits	0	0
Policyholders’ funds		0
Life and Group Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	497	525
Insurance receivables	11	13
Deferred acquisition costs	0	0
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	3,220	3,183
Unearned premiums	120	125
Future policy benefits	10,152	9,490
Policyholders’ funds		0
Corporate and Other Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	2,487	2,753
Insurance receivables	2	2
Deferred acquisition costs	0	0
Goodwill	0	0
Insurance reserves
Claim and claim adjustment expenses	2,644	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