Income Taxes (details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Taxes disclosure
Current income tax expense (benefit) included in consolidated statement of income, federal									$ (176,000,000)	$ 846,000,000	$ 822,000,000
Current income tax expense (benefit) included in consolidated statement of income, foreign									34,000,000	78,000,000	75,000,000
Current income tax expense (benefit) included in consolidated statement of income, state									3,000,000	10,000,000	(8,000,000)
Total current tax expense (benefit)									(139,000,000)	934,000,000	889,000,000
Deferred income tax expense (benefit) included in consolidated statement of income, federal									63,000,000	178,000,000	213,000,000
Deferred income tax expense (benefit) included in consolidated statement of income, foreign									2,000,000	(22,000,000)	(13,000,000)
Total deferred tax expense									65,000,000	156,000,000	200,000,000
Total income tax expense (benefit) included in consolidated statement of income	160,000,000	(1,000,000)	(363,000,000)	130,000,000	303,000,000	366,000,000	211,000,000	210,000,000	(74,000,000)	1,090,000,000	1,089,000,000
Expense (benefit) relating to stock-based compensation, the change in unrealized appreciation on investments, unrealized loss on foreign exchange and unrealized loss on derivatives, and other comprehensive income									399,000,000	(2,000,000)	1,099,000,000
Total income tax expense included in consolidated financial statements									325,000,000	1,088,000,000	2,188,000,000
Income before federal, foreign and state income taxes	778,000,000	332,000,000	(727,000,000)	969,000,000	1,197,000,000	1,371,000,000	881,000,000	857,000,000	1,352,000,000	4,306,000,000	4,711,000,000
Statutory tax rate (percent)									35.00%	35.00%	35.00%
Expected federal income tax expense									473,000,000	1,507,000,000	1,649,000,000
Tax effect of nontaxable investment income									(449,000,000)	(476,000,000)	(480,000,000)
Tax effect of favorable resolution of prior year tax matters									(104,000,000)		(89,000,000)
Tax effect of other, net									6,000,000	59,000,000	9,000,000
Effective tax rate (percent)									(5.00%)	25.00%	23.00%
Current income tax receivable	119,000,000								119,000,000
Current income tax payable					265,000,000					265,000,000
Income, before income taxes, from domestic operations									1,230,000,000	4,200,000,000	4,540,000,000
Income, before income taxes, from foreign operations									122,000,000	106,000,000	171,000,000
Deferred tax assets, claims and claim adjustment expense reserves	936,000,000				996,000,000				936,000,000	996,000,000
Deferred tax assets, unearned premium reserves	680,000,000				662,000,000				680,000,000	662,000,000
Deferred tax assets, other	844,000,000				713,000,000				844,000,000	713,000,000
Total gross deferred tax assets	2,460,000,000				2,371,000,000				2,460,000,000	2,371,000,000
Deferred tax liabilities, deferred acquisition costs	585,000,000				575,000,000				585,000,000	575,000,000
Deferred tax liabilities, investments	1,650,000,000				1,128,000,000				1,650,000,000	1,128,000,000
Deferred tax liabilities, internally-developed software	128,000,000				122,000,000				128,000,000	122,000,000
Deferred tax liabilities, other	90,000,000				53,000,000				90,000,000	53,000,000
Total gross deferred tax liabilities	2,453,000,000				1,878,000,000				2,453,000,000	1,878,000,000
Total deferred income taxes	7,000,000				493,000,000				7,000,000	493,000,000
Net operating loss carryforward on a regular tax basis	59,000,000								59,000,000
Net operating loss carryforward on an alternative minimum tax basis	14,000,000								14,000,000
Alternative minimum tax credit carryforwards available to reduce future federal regular income taxes over an indefinite period	95,000,000								95,000,000
Amount of the Company's foreign operations' undistributed earnings for which U.S. income taxes have not been provided	649,000,000								649,000,000
Unrecognized tax benefits that, if recognized, would affect the annual effective tax rate	2,000,000				3,000,000				2,000,000	3,000,000
Amount of unrecognized tax benefits that are tax positions for which the ultimate deductibility is certain, but for which there is uncertainty about the timing of deductibility	35,000,000				100,000,000				35,000,000	100,000,000
Amount of interest recognized on unrecognized tax benefits in income taxes									(122,000,000)	79,000,000
Accrued payment of interest balance for unrecognized tax benefits	$ 48,000,000				$ 170,000,000				$ 48,000,000	$ 170,000,000