Income Taxes (details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes disclosure
Current income tax expense (benefit) included in consolidated statement of income, federal									$ 406,000,000	$ (176,000,000)	$ 846,000,000
Current income tax expense (benefit) included in consolidated statement of income, foreign									45,000,000	34,000,000	78,000,000
Current income tax expense (benefit) included in consolidated statement of income, state									3,000,000	3,000,000	10,000,000
Total current tax expense (benefit)									454,000,000	(139,000,000)	934,000,000
Deferred income tax expense (benefit) included in consolidated statement of income, federal									223,000,000	63,000,000	178,000,000
Deferred income tax expense (benefit) included in consolidated statement of income, foreign									16,000,000	2,000,000	(22,000,000)
Total deferred tax expense									239,000,000	65,000,000	156,000,000
Total income tax expense (benefit) included in consolidated statement of income	7,000,000	306,000,000	109,000,000	271,000,000	160,000,000	(1,000,000)	(363,000,000)	130,000,000	693,000,000	(74,000,000)	1,090,000,000
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									57,000,000	399,000,000	(2,000,000)
Total income tax expense included in consolidated financial statements									750,000,000	325,000,000	1,088,000,000
Income before federal, foreign and state income taxes	311,000,000	1,170,000,000	608,000,000	1,077,000,000	778,000,000	332,000,000	(727,000,000)	969,000,000	3,166,000,000	1,352,000,000	4,306,000,000
Statutory tax rate (percent)									35.00%	35.00%	35.00%
Expected federal income tax expense									1,108,000,000	473,000,000	1,507,000,000
Tax effect of nontaxable investment income									(427,000,000)	(449,000,000)	(476,000,000)
Tax effect of favorable resolution of prior year tax matters										(104,000,000)
Tax effect of other, net									12,000,000	6,000,000	59,000,000
Effective tax rate (percent)									22.00%	(5.00%)	25.00%
Current income tax receivable					119,000,000					119,000,000
Current income tax payable	102,000,000								102,000,000
Income, before income taxes, from domestic operations									3,000,000,000	1,230,000,000	4,200,000,000
Income, before income taxes, from foreign operations									166,000,000	122,000,000	106,000,000
Deferred tax assets, claims and claim adjustment expense reserves	888,000,000				936,000,000				888,000,000	936,000,000
Deferred tax assets, unearned premium reserves	689,000,000				680,000,000				689,000,000	680,000,000
Deferred tax assets, other	741,000,000				844,000,000				741,000,000	844,000,000
Total gross deferred tax assets	2,318,000,000				2,460,000,000				2,318,000,000	2,460,000,000
Deferred tax liabilities, deferred acquisition costs	590,000,000				585,000,000				590,000,000	585,000,000
Deferred tax liabilities, investments	1,800,000,000				1,650,000,000				1,800,000,000	1,650,000,000
Deferred tax liabilities, internally-developed software	134,000,000				128,000,000				134,000,000	128,000,000
Deferred tax liabilities, other	132,000,000				90,000,000				132,000,000	90,000,000
Total gross deferred tax liabilities	2,656,000,000				2,453,000,000				2,656,000,000	2,453,000,000
Total deferred tax asset					7,000,000					7,000,000
Total deferred tax (liability)	(338,000,000)								(338,000,000)
Net operating loss carryforward on a regular tax basis	37,000,000								37,000,000
Net operating loss carryforward on an alternative minimum tax basis	3,000,000								3,000,000
Alternative minimum tax credit carryforwards available to reduce future federal regular income taxes over an indefinite period	17,000,000								17,000,000
Amount of the Company's foreign operations' undistributed earnings for which U.S. income taxes have not been provided	755,000,000								755,000,000
Unrecognized tax benefits that, if recognized, would affect the annual effective tax rate	3,000,000				2,000,000				3,000,000	2,000,000
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	21,000,000				35,000,000				21,000,000	35,000,000
Amount of interest recognized on unrecognized tax benefits in income taxes									46,000,000	(122,000,000)
Accrued payment of interest balance for unrecognized tax benefits	$ 94,000,000				$ 48,000,000				$ 94,000,000	$ 48,000,000