Segment Information (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	$ 4,519	$ 4,710	$ 13,609	$ 14,202
Net investment income:
Securities available-for-sale and other	1,030	1,062	3,197	3,274
Equity securities, trading	710	(1,890)	1,889	(1,684)
Total net investment income (loss)	1,740	(828)	5,086	1,590
Net realized capital gains (losses)	119	575	(202)	241
Other revenues	64	63	184	188
Total revenues	6,442	4,520	18,677	16,221
Property & Casualty Commercial [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	1,582	1,553	4,691	4,568
Workers' Compensation [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	762	721	2,232	2,071
Property [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	127	129	378	398
Automobiles [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	148	146	440	437
Package Business [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	290	289	871	857
Liability [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	142	135	419	404
Fidelity and Surety [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	53	55	156	164
Professional Liability [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	60	78	195	237
Group Benefits [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	941	1,016	2,879	3,136
Group Disability [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	426	467	1,308	1,460
Group life and accident [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	468	501	1,425	1,529
Other [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	47	48	146	147
Consumer Markets [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	912	930	2,725	2,825
Automobiles [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	632	649	1,894	1,978
Homeowners [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	280	281	831	847
Individual Life [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	207	244	654	665
Variable Life [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	82	122	254	304
Universal Life [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	112	109	360	324
Term / other life [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	13	13	40	37
Retirement Plans [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	91	93	281	291
401(k) [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	79	82	244	254
Government Plans [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	12	11	37	37
Mutual Funds [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	148	153	447	506
Non-proprietary [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	133	138	403	461
Proprietary [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	15	15	44	45
Life Other Operations [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	593	666	1,792	2,050
Property and Casualty Other Operations [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	0	0	(2)	0
Corporate [Member]
Segment Reporting Information [Line Items]
Earned premiums, fees and other considerations	$ 45	$ 55	$ 142	$ 161