Segment Information (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting Information [Line Items]
earned premium, fee income and other considerations	$ 3,922	$ 3,932
Total revenues	4,461	9,024
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	495	(241)
Net investment income:
Securities available-for-sale and other	836	856
Equity securities, trading	(236)	2,562
Total net investment income (loss)	600	3,418
Net realized capital gains (losses)	(86)	1,606
Other revenues	25	68
Total revenues	4,461	9,024
Property & Casualty Commercial [Member]
Segment Reporting Information [Line Items]
Total revenues	1,541	1,529
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	242	253
Net investment income:
Total revenues	1,541	1,529
Workers' Compensation [Member]
Segment Reporting Information [Line Items]
Total revenues	732	733
Net investment income:
Total revenues	732	733
Property [Member]
Segment Reporting Information [Line Items]
Total revenues	136	125
Net investment income:
Total revenues	136	125
Automobiles [Member]
Segment Reporting Information [Line Items]
Total revenues	144	144
Net investment income:
Total revenues	144	144
Package Business [Member]
Segment Reporting Information [Line Items]
Total revenues	283	281
Net investment income:
Total revenues	283	281
Liability [Member]
Segment Reporting Information [Line Items]
Total revenues	145	138
Net investment income:
Total revenues	145	138
Fidelity and Surety [Member]
Segment Reporting Information [Line Items]
Total revenues	51	49
Net investment income:
Total revenues	51	49
Professional Liability [Member]
Segment Reporting Information [Line Items]
Total revenues	50	59
Net investment income:
Total revenues	50	59
Group Benefits [Member]
Segment Reporting Information [Line Items]
Total revenues	799	826
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	51	42
Net investment income:
Total revenues	799	826
Group Disability [Member]
Segment Reporting Information [Line Items]
Total revenues	369	359
Net investment income:
Total revenues	369	359
Group life and accident [Member]
Segment Reporting Information [Line Items]
Total revenues	388	426
Net investment income:
Total revenues	388	426
Other [Member]
Segment Reporting Information [Line Items]
Total revenues	42	41
Net investment income:
Total revenues	42	41
Consumer Markets [Member]
Segment Reporting Information [Line Items]
Total revenues	928	896
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	99	77
Net investment income:
Total revenues	928	896
Automobiles [Member]
Segment Reporting Information [Line Items]
Total revenues	636	619
Net investment income:
Total revenues	636	619
Homeowners [Member]
Segment Reporting Information [Line Items]
Total revenues	292	277
Net investment income:
Total revenues	292	277
Mutual Funds [Member]
Segment Reporting Information [Line Items]
Total revenues	174	160
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	21	18
Net investment income:
Total revenues	174	160
Non-proprietary [Member]
Segment Reporting Information [Line Items]
Total revenues	138	124
Net investment income:
Total revenues	138	124
Proprietary [Member]
Segment Reporting Information [Line Items]
Total revenues	36	36
Net investment income:
Total revenues	36	36
Property and Casualty Other Operations [Member]
Segment Reporting Information [Line Items]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	22	21
Corporate [Member]
Segment Reporting Information [Line Items]
Total revenues	3	3
Net investment income:
Total revenues	$ 3	$ 3