CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Investments
Debt Securities, Available-for-sale, Amortized Cost, Total	$ 41,079.3	$ 40,275.2
Stockholders' Equity
Common Stock, Par Value (in dollars per share)	$ 0.10	$ 0.10
Common Stock, Shares Authorized	725,000,000	725,000,000
Common Stock, Shares Issued	305,813,326	305,104,548
Treasury Stock, Shares at Cost	102,876,514	90,551,513