Consolidated Statements of Financial Position (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Fixed income securities, at fair value, amortized cost (in dollars)	$ 57,525	$ 56,576
Equity securities, at fair value, cost (in dollars)	5,461	5,157
Short-term, at fair value, amortized cost (in dollars)	$ 1,944	$ 4,288
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	25,000,000	25,000,000
Preferred stock, shares issued (in shares)	72,200	72,200
Preferred stock, shares outstanding (in shares)	72,200	72,200
Preferred stock, shares aggregate liquidation preference (in dollars)	$ 1,805	$ 1,805
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	2,000,000,000	2,000,000,000
Common stock, shares issued (in shares)	900,000,000	900,000,000
Common stock, shares outstanding (in shares)	355,000,000	366,000,000
Treasury stock, shares (in shares)	545,000,000	534,000,000