Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 11,108	$ 10,643
Equity securities, cost	3,581	3,368
Land, building and equipment, accumulated depreciation	$ 276	$ 265
Common stock, par value	$ 2	$ 2
common stock, authorized	500.0	500.0
Common stock, issued	198.3	198.3
Common stock, shares outstanding	198.3	198.3
Treasury stock, shares	35.4	35.5