Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Balance Sheets) (Details) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets
Fixed maturity securities available-for-sale, at fair value	$ 39,931	$ 37,571
Short term investments	1,641	2,215
Other assets	779	868
Total assets	55,179	55,331
Liabilities
Short term debt	83	400
Long term debt	2,525	2,251
Other liabilities	2,975	3,056
Total liabilities	43,622	43,807
Equity
Common stock ($2.50 par value; 500,000,000 shares authorized; 273,040,243 shares issued; 269,274,900 and 269,139,198 shares outstanding)	683	683
Additional paid-in capital	2,146	2,200
Retained earnings	8,382	7,876
Accumulated other comprehensive income (loss)	470	326
Treasury stock (3,765,343 and 3,901,045 shares), at cost	(102)	(105)
Notes receivable for the issuance of common stock	(22)	(26)
Total equity	11,557	10,954
Balance Sheet Parenthetical
Common stock, par value	$ 2.50	$ 2.50
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	273,040,243	273,040,243
Common stock, shares outstanding	269,274,900	269,139,198
Treasury stock, shares	3,765,343	3,901,045
Parent Company [Member]
Assets
Investment in subsidiaries	13,564	12,780
Fixed maturity securities available-for-sale, at fair value	2	3
Short term investments	292	215
Amounts due from subsidiaries		11
Surplus note due from subsidiary	250	500
Other assets	18	16
Total assets	14,126	13,525
Liabilities
Short term debt	3	399
Long term debt	2,525	2,131
Other liabilities	41	41
Total liabilities	2,569	2,571
Equity
Common stock ($2.50 par value; 500,000,000 shares authorized; 273,040,243 shares issued; 269,274,900 and 269,139,198 shares outstanding)	683	683
Additional paid-in capital	2,146	2,200
Retained earnings	8,382	7,876
Accumulated other comprehensive income (loss)	470	326
Treasury stock (3,765,343 and 3,901,045 shares), at cost	(102)	(105)
Notes receivable for the issuance of common stock	(22)	(26)
Total equity	11,557	10,954
Total liabilities and equity	14,126	13,525
Balance Sheet Parenthetical
Marketable securities fixed maturities available-for-sale at amortized cost basis	$ 2	$ 3
Common stock, par value	$ 2.50	$ 2.50
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	273,040,243	273,040,243
Common stock, shares outstanding	269,274,900	269,139,198
Treasury stock, shares	3,765,343	3,901,045