Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Short-term investments held as available-for-sale, amortized cost	$ 6,729	$ 9,025
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	275,455,099	274,896,162
Accumulated other comprehensive income (loss), net of deferred tax	24	105
Treasury stock, shares	81,729,792	81,752,966
Non Variable Interest Entities [Member]
Fixed-maturity securities held as available-for-sale, amortized cost	4,412	6,259
Investments pledged as collateral, amortized cost	424	642
Short-term investments held as available-for-sale, amortized cost	1,440	1,577
Other investments, fair value	16	96
Property and equipment, accumulated depreciation	144	139
Medium-term notes, financial instruments carried at fair value	168	165
Variable Interest Entity [Member]
Investments held-to-maturity, fair value	2,867	3,489
Fixed-maturity securities held as available-for-sale, amortized cost	461	473
Variable interest entity notes, financial instruments carried at fair value	$ 3,626	$ 4,754