Condensed Financial Information of Parent Company - Balance Sheets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
Assets
Short Term Investments	$ 2,528	$ 1,893
Taxable Fixed maturities	38,076	37,184
Equity securities	1,663	1,512
Other Invested Assets	1,954	2,180
TOTAL INVESTED ASSETS	44,221	42,769
Other Assets	1,353	1,281
TOTAL ASSETS	52,184	50,445	[1]	49,976
Liabilities
Long Term Debt	3,575	3,575
Dividend Payable to Shareholders	108	107
Accrued Expenses and Other Liabilities	2,188	2,070
TOTAL LIABILITIES	36,357	35,144	[1]
Shareholders' Equity
Preferred Stock - Authorized 8,000,000 Shares; $1 Par Value; Issued - None
Common Stock - Authorized 1,200,000,000 Shares; $1 Par Value; Issued 371,980,460 Shares	372	372
Paid-In Surplus	178	190
Retained Earnings	20,009	18,903	[1]
Accumulated Other Comprehensive Income	1,431	1,195
Treasury Stock, at Cost - 110,217,445 and 99,519,509 Shares	(6,163)	(5,359)
TOTAL SHAREHOLDERS' EQUITY	15,827	15,301	[1]	15,257	[1]
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	52,184	50,445	[1]
Parent Company [Member]
Assets
Short Term Investments	941	1,030
Taxable Fixed maturities	1,309	962
Equity securities	215	179
Other Invested Assets	46	27
TOTAL INVESTED ASSETS	2,511	2,198
Investment in Consolidated Subsidiaries	16,900	16,678
Other Assets	190	188
TOTAL ASSETS	19,601	19,064
Liabilities
Long Term Debt	3,575	3,575
Dividend Payable to Shareholders	108	107
Accrued Expenses and Other Liabilities	91	81
TOTAL LIABILITIES	3,774	3,763
Shareholders' Equity
Preferred Stock - Authorized 8,000,000 Shares; $1 Par Value; Issued - None
Common Stock - Authorized 1,200,000,000 Shares; $1 Par Value; Issued 371,980,460 Shares	372	372
Paid-In Surplus	178	190
Retained Earnings	20,009	18,903
Accumulated Other Comprehensive Income	1,431	1,195
Treasury Stock, at Cost - 110,217,445 and 99,519,509 Shares	(6,163)	(5,359)
TOTAL SHAREHOLDERS' EQUITY	15,827	15,301
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ 19,601	$ 19,064

[1] As Adjusted