Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Short-term investments held as available-for-sale, amortized cost	$ 9,025	$ 12,822
Variable interest entity notes, financial instruments carried at fair value	4,800
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	274,896,162	274,719,578
Accumulated other comprehensive loss, deferred tax	105	229
Treasury stock, shares	81,752,966	74,973,978
Non Variable Interest Entities [Member]
Fixed-maturity securities held as available-for-sale, amortized cost	6,259	9,679
Investments pledged as collateral, amortized cost	642	548
Short-term investments held as available-for-sale, amortized cost	1,577	2,073
Other investments, fair value	96	185
Property and equipment, accumulated depreciation	139	135
Medium-term notes, financial instruments carried at fair value	165	116
Variable Interest Entities [Member]
Investments held-to-maturity, fair value	3,489	3,760
Fixed-maturity securities held as available-for-sale, amortized cost	473	338
Variable interest entity notes, financial instruments carried at fair value	$ 4,754	$ 6,680