Segment Information (Schedule Of Segment Information) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013 industry segment	Dec. 31, 2012	Dec. 31, 2011
Accounting Policies [Abstract]
Number of Industries Operated In									2
Number of Insurance Segments									4
Segment Reporting Information [Line Items]
Revenues	$ 1,172	$ 1,152	$ 1,104	$ 1,103	$ 1,070	$ 1,035	$ 1,020	$ 986	$ 4,531	$ 4,111	$ 3,803
Net Investment Income									529	531	525
Realized gains on investments									83	42	70
Income (loss) before income taxes	167	182	148	217	273	152	29	112	714	566	173
Identifiable assets	17,662				16,548				17,662	16,548
Property Casualty Insurance Segment [Member]
Segment Reporting Information [Line Items]
Identifiable assets	2,455				2,395				2,455	2,395
Commercial Lines [Member]
Segment Reporting Information [Line Items]
Revenues									2,639	2,387	2,200
Income (loss) before income taxes									186	181	(102)
Commercial Lines [Member] | Commercial Casualty Segment [Member]
Segment Reporting Information [Line Items]
Revenues									856	767	711
Commercial Lines [Member] | Commercial Property Segment
Segment Reporting Information [Line Items]
Revenues									623	545	497
Commercial Lines [Member] | Commercial Auto Segment
Segment Reporting Information [Line Items]
Revenues									479	426	394
Commercial Lines [Member] | Workers' Compensation [Member]
Segment Reporting Information [Line Items]
Revenues									365	344	318
Commercial Lines [Member] | Specialty Packages
Segment Reporting Information [Line Items]
Revenues									150	151	138
Commercial Lines [Member] | Management Liability and Surety
Segment Reporting Information [Line Items]
Revenues									119	111	103
Commercial Lines [Member] | Machinery and Equipment
Segment Reporting Information [Line Items]
Revenues									44	39	36
Commercial Lines [Member] | Commercial Lines Insurance Premiums [Member]
Segment Reporting Information [Line Items]
Revenues									2,636	2,383	2,197
Commercial Lines [Member] | Other Fee Revenue
Segment Reporting Information [Line Items]
Revenues									3	4	3
Personal Lines [Member]
Segment Reporting Information [Line Items]
Revenues									962	870	763
Income (loss) before income taxes									33	(43)	(182)
Personal Lines [Member] | Personal Auto
Segment Reporting Information [Line Items]
Revenues									443	404	368
Personal Lines [Member] | Home Owner Segment
Segment Reporting Information [Line Items]
Revenues									403	353	294
Personal Lines [Member] | Other Personal Lines [Member]
Segment Reporting Information [Line Items]
Revenues									115	111	100
Personal Lines [Member] | Commercial Lines Insurance Premiums [Member]
Segment Reporting Information [Line Items]
Revenues									961	868	762
Personal Lines [Member] | Other Fee Revenue
Segment Reporting Information [Line Items]
Revenues									1	2	1
Excess And Surplus Lines Insurance [Member]
Segment Reporting Information [Line Items]
Revenues									116	93	70
Income (loss) before income taxes									14	(1)	6
Life Insurance Segment [Member]
Segment Reporting Information [Line Items]
Revenues									189	178	165
Income (loss) before income taxes									9	(3)	(3)
Identifiable assets	1,225				1,201				1,225	1,201
Total Life Insurance [Member]
Segment Reporting Information [Line Items]
Revenues									193	179	167
Total Life Insurance [Member] | Separate Account Investment Management Fees [Member]
Segment Reporting Information [Line Items]
Revenues									4	1	2
Investments Segment [Member]
Segment Reporting Information [Line Items]
Revenues									612	573	595
Income (loss) before income taxes									532	491	514
Identifiable assets	13,618				12,599				13,618	12,599
Investments Segment [Member] | Investment Income, Net Of Expenses [Member]
Segment Reporting Information [Line Items]
Net Investment Income									529	531	525
Investments Segment [Member] | Realized Investment Gains [Member]
Segment Reporting Information [Line Items]
Realized gains on investments									83	42	70
Other [Member]
Segment Reporting Information [Line Items]
Revenues									9	9	8
Income (loss) before income taxes									(60)	(59)	(60)
Identifiable assets	$ 364				$ 353				$ 364	$ 353