Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Statement Of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 8,222	$ 8,084
Equity securities, cost	2,369	2,162
Land, building and equipment, accumulated depreciation	$ 397	$ 376
Common stock, par value	$ 2	$ 2
Common stock, authorized	500	500
Common stock, issued	197	196
Common stock, shares outstanding	197	196
Treasury stock, shares	34	34