CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Investments
Fixed Maturity Securities, Amortized Cost	$ 40,474.2	$ 40,275.2
Stockholders' Equity
Common Stock, Par	$ 0.10	$ 0.10
Common Stock, Authorized	725,000,000	725,000,000
Common Stock, Issued	305,565,569	305,104,548
Treasury Stock, Shares at Cost	93,275,293	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
-Publisher FASB
-Name Accounting Standards Codification
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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