Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash Flows from Operating Activities
Net income	$ 1,443	$ 1,226
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Increase in Unpaid Losses and Loss Expenses, Net	237	728
Increase in Unearned Premiums, Net	51	94
Decrease in Premiums Receivable	82	101
Change in Income Tax Payable or Recoverable	(1)	(193)
Amortization of Premiums and Discounts on Fixed Maturities	121	111
Depreciation	39	41
Realized Investment Gains, Net	(103)	(300)
Other, Net	(29)	(118)
Net Cash Provided by Operating Activities	1,840	1,690
Cash Flows from Investing Activities
Proceeds from Fixed Maturities - Sales	1,838	1,184
Proceeds from Fixed Maturities - Maturities, Calls and Redemptions	2,985	2,450
Proceeds from Sales of Equity Securities	128	103
Purchases of Fixed Maturities	(5,505)	(3,660)
Purchases of Equity Securities	(88)	(67)
Investments in Other Invested Assets, Net	248	198
Increase in Short Term Investments, Net	(384)	(378)
Increase in Net Payable from Security Transactions Not Settled	136	91
Purchases of Property and Equipment, Net	(31)	(30)
Net Cash Used in Investing Activities	(673)	(109)
Cash Flows from Financing Activities
Increase (Decrease) in Funds Held Under Deposit Contracts	(8)	8
Proceeds from Issuance of Common Stock Under Stock-Based Employee Compensation Plans	68	63
Repurchase of Shares	(903)	(1,327)
Dividends Paid to Shareholders	(329)	(340)
Net Cash Used in Financing Activities	(1,172)	(1,596)
Net Decrease in Cash	(5)	(15)
Cash at Beginning of Year	58	70
Cash at End of Period	$ 53	$ 55