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Consolidated Balance Sheets - (Parenthetical) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Statement of Financial Position [Abstract] |  |
Fixed maturities securities at amortized cost | $ 38,215 | $ 38,361
Equity securities at cost | 659 | 106
Allowance for uncollectible reinsurance | 29 | 37
Allowance for uncollectible insurance receivables | 44 | 46
Accumulated depreciation on property and equipment | 274 | 254
Due to related parties | $ 143 | $ 50
Common stock, par value (in usd per share) | $ 2.50 | $ 2.50
Common stock, shares authorized (in shares) | 500,000,000 | 500,000,000
Common stock, shares issued (in shares) | 273,040,243 | 273,040,243
Common stock, shares outstanding (in shares) | 271,205,390 | 270,495,998
Treasury stock, shares (in shares) | 1,834,853 | 2,544,245

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