Consolidated Balance Sheets - (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
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