Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Fixed-maturity securities held as available-for-sale, amortized cost	$ 6,224	$ 6,160
Preferred stock, par value	$ 1	$ 1
Preferred stock, authorized shares	10,000,000	10,000,000
Preferred stock, issued	0	0
Preferred stock, outstanding	0	0
Common stock, par value	$ 1	$ 1
Common stock, authorized shares	400,000,000	400,000,000
Common stock, issued shares	283,390,167	281,833,618
Treasury stock, shares	146,112,863	130,303,241
Non Variable Interest Entity [Member]
Fixed-maturity securities held as available-for-sale, amortized cost	$ 5,120	$ 5,155
Investments pledged as collateral, amortized cost	216	322
Short-term investments held as available-for-sale, amortized cost	931	720
Other investments, fair value	6	13
Medium-term notes, financial instruments carried at fair value	165	161
Accumulated other comprehensive income (loss), taxes	15	51
Variable Interest Entity Primary Beneficiary [Member]
Investments held-to-maturity, fair value	525	2,401
Variable interest entity notes, financial instruments carried at fair value	$ 2,204	$ 2,362