Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Balance Sheets) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets
Cash	$ 387	$ 190	$ 195	$ 156
Fixed maturity securities available-for-sale, at fair value (amortized cost of $0 and $1)	39,569	40,749
Short term investments	1,660	1,706
Other assets	1,297	841
Total assets	55,047	55,566
Liabilities
Short term debt	350	0
Long term debt	2,212	2,559
Other liabilities	4,243	3,833
Total liabilities	43,291	42,772
Stockholders' Equity
Common stock ($2.50 par value; 500,000,000 shares authorized; 273,040,243 shares issued; 270,274,361 and 269,980,202 shares outstanding)	683	683	683	683
Additional paid-in capital	2,153	2,151	2,145	2,146
Retained earnings	9,313	9,645	9,495	8,774
Accumulated other comprehensive income (loss)	(315)	400	442	831
Treasury stock (2,765,882 and 3,060,041 shares), at cost	(78)	(84)	(91)	(99)
Notes receivable for the issuance of common stock	0	(1)	(23)	(21)
Total stockholders’ equity	11,756	12,794	12,651
Total liabilities and stockholders' equity	55,047	55,566
Balance Sheet Parenthetical
Marketable securities fixed maturities available-for-sale at amortized cost basis	$ 37,250	$ 37,316
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	270,274,361	269,980,202
Treasury stock, shares	2,765,882	3,060,041
Parent Company [Member]
Assets
Investment in subsidiaries	$ 13,851	$ 14,867
Cash	4	1	$ 1	$ 0
Fixed maturity securities available-for-sale, at fair value (amortized cost of $0 and $1)	0	1
Short term investments	478	499
Other assets	3	3
Total assets	14,336	15,371
Liabilities
Short term debt	350	0
Long term debt	2,182	2,529
Other liabilities	48	48
Total liabilities	2,580	2,577
Stockholders' Equity
Common stock ($2.50 par value; 500,000,000 shares authorized; 273,040,243 shares issued; 270,274,361 and 269,980,202 shares outstanding)	683	683
Additional paid-in capital	2,153	2,151
Retained earnings	9,313	9,645
Accumulated other comprehensive income (loss)	(315)	400
Treasury stock (2,765,882 and 3,060,041 shares), at cost	(78)	(84)
Notes receivable for the issuance of common stock	0	(1)
Total stockholders’ equity	11,756	12,794
Total liabilities and stockholders' equity	14,336	15,371
Balance Sheet Parenthetical
Marketable securities fixed maturities available-for-sale at amortized cost basis	$ 0	$ 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	270,274,361	269,980,202
Treasury stock, shares	2,765,882	3,060,041