Segment Information (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	$ 3,992	$ 4,505	$ 7,943	$ 9,071
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(190)	(101)	(431)	(5)
Net investment income:
Securities available-for-sale and other	867	1,094	1,723	2,161
Equity securities, trading	1,189	(1,662)	3,751	1,099
Total net investment income (loss)	2,056	(568)	5,474	3,260
Net realized capital gains (losses)	(648)	567	958	(361)
Other revenues	65	61	133	120
Total revenues	5,465	4,565	14,508	12,090
Property & Casualty Commercial [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	1,545	1,552	3,074	3,109
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	192	149	445	338
Workers' Compensation [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	741	737	1,474	1,470
Property [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	127	126	252	251
Automobiles [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	144	146	288	292
Package Business [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	285	289	566	581
Liability [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	141	136	279	277
Fidelity and Surety [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	52	51	101	103
Professional Liability [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	55	67	114	135
Group Benefits [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	838	966	1,664	1,938
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	61	35	103	53
Group Disability [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	370	439	729	882
Group life and accident [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	428	478	854	957
Other [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	40	49	81	99
Consumer Markets [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	908	904	1,804	1,813
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	15	(50)	92	58
Automobiles [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	626	630	1,245	1,262
Homeowners [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	282	274	559	551
Mutual Funds [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	170	148	334	299
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	20	18	38	38
Non-proprietary [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	132	120	261	243
Proprietary [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	38	28	73	56
Property and Casualty Other Operations [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	0	(2)	0	(2)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(71)	(15)	(50)	12
Corporate [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	$ 2	$ 45	$ 5	$ 97