Condensed Consolidated Balance Sheets - (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Amortized cost	$ 38,814	$ 38,361
Cost	118	106
Allowance for uncollectible reinsurance	37	37
Allowance for uncollectible insurance receivables	46	46
Accumulated depreciation	275	254
Due to related parties	$ 25	$ 50
Common stock, par value (dollars 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)	271,176,870	270,495,998
Treasury stock, share (in shares)	1,863,373	2,544,245