CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Investments
Fixed Maturity Securities, Amortized Cost	$ 40,789.7	$ 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	305,751,664	305,104,548
Treasury Stock, Shares at Cost	99,523,062	90,551,513

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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