CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Investments
Fixed Maturity Securities, Amortized Cost	$ 39,817.2	$ 39,780.5
Stockholders' Equity
Common Stock, Par	$ 0.10	$ 0.10
Common Stock, Authorized	725,000,000	725,000,000
Common Stock, Issued	305,029,229	304,448,032
Treasury Stock, Shares at Cost	86,347,280	81,900,950

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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