Condensed Consolidated Balance Sheets - (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Amortized cost	$ 38,269	$ 38,361
Cost	112	106
Allowance for uncollectible reinsurance	38	37
Allowance for uncollectible insurance receivables	47	46
Accumulated depreciation	255	254
Due to related parties	$ 41	$ 50
Common stock, par value (dollars per share)	$ 2.50	$ 2.50
Common stock, shares authorized (shares)	500,000,000	500,000,000
Common stock, shares issued (shares)	273,040,243	273,040,243
Common stock, shares outstanding (shares)	270,978,126	270,495,998
Treasury stock, share (shares)	2,062,117	2,544,245