Consolidated Balance Sheet Parentheticals (Unaudited at March 31, 2018) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Fixed maturities, available for sale, amortized cost	$ 62,093	$ 61,316
Equity securities, cost	$ 431
Equity securities, available for sale, cost		$ 440
Common stock, shares authorized (in shares)	1,750,000,000.0	1,750,000,000.0
Common stock, shares issued (in shares)	270,300,000	271,500,000
Common stock, shares outstanding (in shares)	270,200,000	271,400,000
Treasury stock, at cost (in shares)	503,700,000	500,900,000