Shareholders' Equity (Components Of Accumulated Other Comprehensive Income (Loss)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Balance, beginning	$ 230	$ (419)	$ (3,586)
Acquisition of CNA Surety noncontrolling interests and disposition of FICOH ownership interest	10
Adjustment to initially apply accounting guidance for other-than-temporary impairment losses, after tax			(122)
Unrealized holding gains (losses) on investments, after tax	344	698	3,071
Adjustment for items included in Net income, after tax	58	(55)	478
Foreign currency translation adjustment	(14)	49	117
Pension liability adjustment, after tax	(238)	29	6
Amounts attributable to noncontrolling interests	(15)	(72)	(383)
Balance, ending	375	230	(419)
Unrealized Gains (Losses) On Investments [Member]
Balance, beginning	607	173	(3,092)
Acquisition of CNA Surety noncontrolling interests and disposition of FICOH ownership interest	2
Adjustment to initially apply accounting guidance for other-than-temporary impairment losses, after tax			(58)
Unrealized holding gains (losses) on investments, after tax	368	585	3,212
Adjustment for items included in Net income, after tax	(15)	(89)	499
Amounts attributable to noncontrolling interests	(42)	(62)	(388)
Balance, ending	920	607	173
Adjustment to initially apply accounting guidance for other-than-temporary impairment losses, tax amount			(31)
Unrealized holding gains (losses) on investments, tax amount	(206)	(319)	(1,756)
Adjustment for items included in Net income, tax amount	8	48	(269)
OTTI Losses [Member]
Balance, beginning	(65)	(144)
Adjustment to initially apply accounting guidance for other-than-temporary impairment losses, after tax			(64)
Unrealized holding gains (losses) on investments, after tax	(44)	59	(190)
Adjustment for items included in Net income, after tax	54	27	95
Amounts attributable to noncontrolling interests	(2)	(7)	15
Balance, ending	(57)	(65)	(144)
Adjustment to initially apply accounting guidance for other-than-temporary impairment losses, tax amount			(34)
Unrealized holding gains (losses) on investments, tax amount	23	(32)	103
Adjustment for items included in Net income, tax amount	(29)	(15)	(51)
Cash Flow Hedges [Member]
Balance, beginning	(18)	(81)	(16)
Unrealized holding gains (losses) on investments, after tax	20	54	49
Adjustment for items included in Net income, after tax	19	7	(116)
Amounts attributable to noncontrolling interests	4	2	2
Balance, ending	25	(18)	(81)
Unrealized holding gains (losses) on investments, tax amount	(13)	(30)	(26)
Adjustment for items included in Net income, tax amount	(10)	(4)	63
Foreign Currency Translation [Member]
Balance, beginning	121	77	(28)
Foreign currency translation adjustment	(14)	49	117
Amounts attributable to noncontrolling interests	1	(5)	(12)
Balance, ending	108	121	77
Pension Liability [Member]
Balance, beginning	(415)	(444)	(450)
Acquisition of CNA Surety noncontrolling interests and disposition of FICOH ownership interest	8
Pension liability adjustment, after tax	(238)	29	6
Amounts attributable to noncontrolling interests	24
Balance, ending	(621)	(415)	(444)
Pension liability adjustment, tax amount	$ 126	$ (15)	$ (7)