CONSOLIDATED BALANCE SHEET (unaudited) (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Investments:
Fixed maturities, available for sale, amortized cost	$ 20,092.5	$ 19,803.1
Equity securities cost	$ 688.7	$ 580.7
Shareholders' equity:
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	8,000,000,000	8,000,000,000
Common stock, shares issued (in shares)	167,762,323	173,753,614
Common stock, shares outstanding (in shares)	167,762,323	173,753,614