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, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets
Cash	$ 190	$ 195	$ 156	$ 75
Fixed maturity securities available-for-sale, at fair value (amortized cost of $1 and $1)	40,749	41,197
Short term investments	1,706	1,407
Other assets	841	969
Total assets	55,566	57,194
Liabilities
Short term debt		549
Long term debt	2,559	2,011
Other liabilities	3,833	3,408
Total liabilities	42,772	44,543
Stockholders' Equity
Common stock ($2.50 par value; 500,000,000 shares authorized; 273,040,243 shares issued; 269,980,202 and 269,717,583 shares outstanding)	683	683
Additional paid-in capital	2,151	2,145
Retained earnings	9,645	9,495
Accumulated other comprehensive income (loss)	400	442	831
Treasury stock (3,060,041 and 3,322,660 shares), at cost	(84)	(91)
Notes receivable for the issuance of common stock	(1)	(23)
Total stockholders’ equity	12,794	12,651	12,314
Total liabilities and stockholders' equity	55,566	57,194
Balance Sheet Parenthetical
Marketable securities fixed maturities available-for-sale at amortized cost basis	37,316	39,275
Common stock, par value	$ 0	$ 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	269,980,202	269,717,583
Treasury stock, shares	3,060,041	3,322,660
Parent Company [Member]
Assets
Investment in subsidiaries	14,867	14,708
Cash	1	1
Fixed maturity securities available-for-sale, at fair value (amortized cost of $1 and $1)	1	1
Short term investments	499	505
Amounts due from subsidiaries		3
Other assets	3	3
Total assets	15,371	15,221
Liabilities
Short term debt		549
Long term debt	2,529	1,981
Other liabilities	48	40
Total liabilities	2,577	2,570
Stockholders' Equity
Common stock ($2.50 par value; 500,000,000 shares authorized; 273,040,243 shares issued; 269,980,202 and 269,717,583 shares outstanding)	683	683
Additional paid-in capital	2,151	2,145
Retained earnings	9,645	9,495
Accumulated other comprehensive income (loss)	400	442
Treasury stock (3,060,041 and 3,322,660 shares), at cost	(84)	(91)
Notes receivable for the issuance of common stock	(1)	(23)
Total stockholders’ equity	12,794	12,651
Total liabilities and stockholders' equity	15,371	15,221
Balance Sheet Parenthetical
Marketable securities fixed maturities available-for-sale at amortized cost basis	$ 1	$ 1
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	269,980,202	269,717,583
Treasury stock, shares	3,060,041	3,322,660