Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Short-term investments held as available-for-sale, amortized cost	$ 7,306	$ 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	275,479,642	274,896,162
Accumulated other comprehensive loss, net of deferred tax	9	105
Treasury stock, shares	81,732,274	81,752,966
Non Variable Interest Entities [Member]
Fixed-maturity securities held as available-for-sale, amortized cost	4,724	6,259
Investments pledged as collateral, amortized cost	397	642
Short-term investments held as available-for-sale, amortized cost	1,591	1,577
Other investments, fair value	50	96
Property and equipment, accumulated depreciation	142	139
Medium-term notes, financial instruments carried at fair value	151	165
Variable Interest Entity [Member]
Investments held-to-maturity, fair value	2,896	3,489
Fixed-maturity securities held as available-for-sale, amortized cost	567	473
Variable interest entity notes, financial instruments carried at fair value	$ 3,638	$ 4,754