Condensed Consolidated Balance Sheets - (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Fixed maturities securities at amortized cost	$ 37,991	$ 38,215
Equity securities at cost	749	659
Allowance for uncollectible reinsurance	29	29
Allowance for uncollectible insurance receivables	43	44
Accumulated depreciation on property and equipment	253	274
Due to related parties	$ 147	$ 143
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)	271,371,607	271,205,390
Treasury stock, shares (in shares)	1,668,636	1,834,853