Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Debt Securities, Available-for-sale, Amortized Cost	$ 11,478	$ 11,312
Equity securities, cost	3,938	3,927
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	$ 290	$ 285
Common Stock, Par or Stated Value Per Share	$ 2	$ 2
Common Stock, Shares Authorized	500.0	500.0
Common Stock, Shares, Issued	198.3	198.3
Treasury Stock, Shares	37.3	37.4