Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
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	277,793,696	277,405,039
Accumulated other comprehensive income (loss), net of deferred tax	$ 18	$ 21
Treasury stock, shares	84,836,010	81,733,530
Non Variable Interest Entities [Member]
Fixed-maturity securities held as available-for-sale, amortized cost	4,101	4,347
Investments pledged as collateral, amortized cost	374	489
Short-term investments held as available-for-sale, amortized cost	859	662
Other investments, fair value	13	12
Property and equipment, accumulated depreciation	144	146
Medium-term notes, financial instruments carried at fair value	181	165
Variable Interest Entity [Member]
Investments held-to-maturity, fair value	2,759	2,674
Fixed-maturity securities held as available-for-sale, amortized cost	628	637
Variable interest entity notes, financial instruments carried at fair value	$ 3,578	$ 3,659