Segment Information (details) (USD $) In Millions	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Segment reporting information
Premiums	$ 5,503	$ 5,340	$ 10,874	$ 10,570
Net investment income	758	762	1,537	1,515
Fee income	74	76	148	155
Other revenues	34	32	68	64
Operating income (loss)	(377)	690	449	1,321
After-tax interest expense	63	63	125	127
Segment Information disclosure
Net realized investment gains (losses)	19	(31)	39	(6)
Total revenues	6,388	6,179	12,666	12,298
Operating income (loss)	(377)	690	449	1,321
Net realized investment gains (losses), net of tax	13	(20)	26	(4)
Net income (loss)	(364)	670	475	1,317
Total reportable segments
Segment reporting information
Premiums	5,503	5,340	10,874	10,570
Net investment income	758	762	1,537	1,515
Fee income	74	76	148	155
Other revenues	34	32	68	64
Total operating revenues	6,369	6,210	12,627	12,304
Operating income (loss)	(296)	758	598	1,470
Segment Information disclosure
Operating income (loss)	(296)	758	598	1,470
Business Insurance
Segment reporting information
Premiums	2,802	2,663	5,547	5,291
Net investment income	541	537	1,097	1,065
Fee income	74	76	148	155
Other revenues	10	7	19	13
Total operating revenues	3,427	3,283	6,811	6,524
Operating income (loss)	11	567	615	1,134
Segment Information disclosure
Operating income (loss)	11	567	615	1,134
Workers' compensation
Segment reporting information
Premiums	712	605	1,392	1,205
Commercial automobile
Segment reporting information
Premiums	480	471	953	942
Property
Segment reporting information
Premiums	401	423	802	846
Business Insurance, General liability
Segment reporting information
Premiums	429	433	857	858
Commercial multi-peril
Segment reporting information
Premiums	778	730	1,540	1,440
Business Insurance, Other
Segment reporting information
Premiums	2	1	3
Financial, Professional & International Insurance
Segment reporting information
Premiums	810	855	1,583	1,679
Net investment income	105	110	211	221
Other revenues	6	7	13	13
Total operating revenues	921	972	1,807	1,913
Operating income (loss)	164	172	284	258
Segment Information disclosure
Operating income (loss)	164	172	284	258
Fidelity and surety
Segment reporting information
Premiums	250	286	484	533
Financial, Professional & International Insurance, General liability
Segment reporting information
Premiums	216	222	424	448
International
Segment reporting information
Premiums	311	313	609	631
Financial, Professional & International Insurance, Other
Segment reporting information
Premiums	33	34	66	67
Personal Insurance
Segment reporting information
Premiums	1,891	1,822	3,744	3,600
Net investment income	112	115	229	229
Other revenues	18	18	36	38
Total operating revenues	2,021	1,955	4,009	3,867
Operating income (loss)	(471)	19	(301)	78
Segment Information disclosure
Operating income (loss)	(471)	19	(301)	78
Automobile
Segment reporting information
Premiums	931	921	1,846	1,825
Homeowners and other
Segment reporting information
Premiums	960	901	1,898	1,775
Interest Expense and Other
Segment reporting information
Operating income (loss)	(81)	(68)	(149)	(149)
Segment Information disclosure
Operating income (loss)	$ (81)	$ (68)	$ (149)	$ (149)

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