Segment Information (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
earned premium, fee income and other considerations	$ 3,821	$ 3,807	$ 7,619	$ 7,570
Total revenues	4,616	4,734	9,228	11,034
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(467)	(190)	28	(431)
Net investment income:
Net investment income (loss)	768	841	1,592	1,666
Net realized capital gains (losses)	(4)	21	(39)	1,665
Other revenues	31	65	56	133
Total revenues	4,616	4,734	9,228	11,034
Property & Casualty Commercial [Member]
Segment Reporting Information [Line Items]
Total revenues	1,559	1,545	3,100	3,074
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	199	192	441	445
Net investment income:
Total revenues	1,559	1,545	3,100	3,074
Workers' Compensation [Member]
Segment Reporting Information [Line Items]
Total revenues	734	741	1,466	1,474
Net investment income:
Total revenues	734	741	1,466	1,474
Property [Member]
Segment Reporting Information [Line Items]
Total revenues	137	127	273	252
Net investment income:
Total revenues	137	127	273	252
Automobiles [Member]
Segment Reporting Information [Line Items]
Total revenues	145	144	289	288
Net investment income:
Total revenues	145	144	289	288
Package Business [Member]
Segment Reporting Information [Line Items]
Total revenues	289	285	572	566
Net investment income:
Total revenues	289	285	572	566
Liability [Member]
Segment Reporting Information [Line Items]
Total revenues	146	141	291	279
Net investment income:
Total revenues	146	141	291	279
Fidelity and Surety [Member]
Segment Reporting Information [Line Items]
Total revenues	52	52	103	101
Net investment income:
Total revenues	52	52	103	101
Professional Liability [Member]
Segment Reporting Information [Line Items]
Total revenues	56	55	106	114
Net investment income:
Total revenues	56	55	106	114
Group Benefits [Member]
Segment Reporting Information [Line Items]
Total revenues	777	838	1,576	1,664
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	55	61	106	103
Net investment income:
Total revenues	777	838	1,576	1,664
Group Disability [Member]
Segment Reporting Information [Line Items]
Total revenues	365	370	734	729
Net investment income:
Total revenues	365	370	734	729
Group life and accident [Member]
Segment Reporting Information [Line Items]
Total revenues	371	428	759	854
Net investment income:
Total revenues	371	428	759	854
Other [Member]
Segment Reporting Information [Line Items]
Total revenues	41	40	83	81
Net investment income:
Total revenues	41	40	83	81
Consumer Markets [Member]
Segment Reporting Information [Line Items]
Total revenues	946	908	1,874	1,804
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(30)	15	69	92
Net investment income:
Total revenues	946	908	1,874	1,804
Automobiles [Member]
Segment Reporting Information [Line Items]
Total revenues	650	626	1,286	1,245
Net investment income:
Total revenues	650	626	1,286	1,245
Homeowners [Member]
Segment Reporting Information [Line Items]
Total revenues	296	282	588	559
Net investment income:
Total revenues	296	282	588	559
Mutual Funds [Member]
Segment Reporting Information [Line Items]
Total revenues	183	165	357	325
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	21	20	42	38
Net investment income:
Total revenues	183	165	357	325
Non-proprietary [Member]
Segment Reporting Information [Line Items]
Total revenues	148	128	286	252
Net investment income:
Total revenues	148	128	286	252
Proprietary [Member]
Segment Reporting Information [Line Items]
Total revenues	35	37	71	73
Net investment income:
Total revenues	35	37	71	73
Life Other Operations [Member]
Segment Reporting Information [Line Items]
Total revenues	352	349	705	698
Net investment income:
Total revenues	352	349	705	698
Property and Casualty Other Operations [Member]
Segment Reporting Information [Line Items]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(144)	(71)	(122)	(50)
Corporate [Member]
Segment Reporting Information [Line Items]
Total revenues	4	2	7	5
Net investment income:
Total revenues	$ 4	$ 2	$ 7	$ 5