CONSOLIDATED BALANCE SHEET (unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Investments:
Fixed maturities, available for sale, amortized cost	$ 20,820.9	$ 20,702.1
Equity securities cost	$ 504.4	$ 420.0
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)	167,354,255	166,857,931
Common stock, shares outstanding (in shares)	167,354,255	166,857,931