Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities
Net income	$ 1,585	$ 3,108	$ 2,549
Adjustments to reconcile net income to net cash flows from operating activities
Net realized losses (gains)	795	(432)	196
Amortization of premiums/discounts on fixed maturities	152	145	53
Deferred income taxes	19	116	(19)
Unpaid losses and loss expenses	43	(360)	298
Unearned premiums	9	262	102
Future policy benefits	78	48	67
Insurance and reinsurance balances payable	216	(172)	434
Accounts payable, accrued expenses, and other liabilities	39	130	(206)
Income taxes payable	39	10	13
Insurance and reinsurance balances receivable	(217)	50	(119)
Reinsurance recoverable on losses and loss expenses	531	626	518
Reinsurance recoverable on policy benefits	25	49	(51)
Deferred policy acquisition costs	(160)	(193)	(309)
Prepaid reinsurance premiums	(34)	(13)	24
Other	350	172	(215)
Net cash flows from operating activities	3,470	3,546	3,335
Cash flows from investing activities
Purchases of fixed maturities available for sale	(23,823)	(29,985)	(31,789)
Purchases of to be announced mortgage-backed securities	(755)	(1,271)	(5,471)
Purchases of fixed maturities held to maturity	(340)	(616)	(472)
Purchases of equity securities	(309)	(794)	(354)
Sales of fixed maturities available for sale	17,176	23,096	23,693
Sales of to be announced mortgage-backed securities	795	1,183	5,961
Sales of fixed maturities held to maturity			11
Sales of equity securities	376	774	1,272
Maturities and redemptions of fixed maturities available for sale	3,720	3,660	3,404
Maturities and redemptions of fixed maturities held to maturity	1,279	1,353	514
Net derivative instruments settlements	(67)	(109)	(92)
Acquisition of subsidiaries (net of cash acquired of $91 in 2011 and $80 in 2010)	(606)	(1,139)
Other	(482)	(333)	99
Net cash flows used for investing activities	(3,036)	(4,181)	(3,224)
Cash flows from financing activities
Dividends paid on Common Shares	(459)	(435)	(388)
Common Shares repurchased	(195)	(235)
Proceeds from issuance of short-term debt	5,238	1,300
Repayment of short-term debt	(5,288)	(159)	(466)
Proceeds from issuance of long-term debt		699	500
Repayment of long-term debt		(500)
Proceeds from share-based compensation plans	133	63	25
Tax benefit (expense) on share-based compensation expense	6	(1)	8
Net cash flows (used for) from financing activities	(565)	732	(321)
Effect of foreign currency rate changes on cash and cash equivalents	(27)	6	12
Net (decrease) increase in cash	(158)	103	(198)
Cash - beginning of year	772	669	867
Cash - end of year	614	772	669
Supplemental cash flow information
Taxes paid	460	434	538
Interest paid	$ 234	$ 204	$ 228