Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Cash Flows from Operating Activities [Abstract]
Net Income	$ 910	$ 928
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities [Abstract]
Increase in Unpaid Losses and Loss Expenses, Net	279	402
Increase in Unearned Premiums, Net	115	147
Increase in Premiums Receivable	(118)	(129)
Change in Income Tax Payable or Recoverable	(100)	(174)
Amortization of Premiums and Discounts on Fixed Maturities	77	75
Depreciation	26	29
Realized Investment Gains, Net	(103)	(229)
Other, Net	(200)	(216)
Net Cash Provided by Operating Activities	886	833
Cash Flows from Investing Activities [Abstract]
Proceeds from Fixed Maturities - Sales	1,176	832
Proceeds from Fixed Maturities - Maturities, Calls and Redemptions	1,946	1,445
Proceeds from Sales of Equity Securities	63	66
Purchases of Fixed Maturities	(3,477)	(2,629)
Purchases of Equity Securities	(70)	(61)
Investments in Other Invested Assets, Net	179	128
Decrease (Increase) in Short Term Investments, Net	(117)	221
Increase in Net Payable from Security Transactions Not Settled	221	200
Purchases of Property and Equipment, Net	(21)	(19)
Net Cash Provided by (Used in) Investing Activities	(100)	183
Cash Flows from Financing Activities [Abstract]
Increase (Decrease) in Funds Held Under Deposit Contracts	(6)	11
Proceeds from Issuance of Common Stock Under Stock-Based Employee Compensation Plans	60	56
Repurchase of Shares	(618)	(855)
Dividends Paid to Shareholders	(219)	(227)
Net Cash Used in Financing Activities	(783)	(1,015)
Net Increase in Cash	3	1
Cash at Beginning of Year	58	70
Cash at End of Period	$ 61	$ 71