CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Stockholders' Equity [Abstract]
Change in unrealized appreciation (depreciation) of investments, applicable income tax expense (benefit)	$ 93.8	$ (82.3)	$ 349.1	$ (221.2)
Change in noncredit component of impairment losses on fixed maturities, available for sale, applicable income tax expense (benefit)	$ 1.5	$ (0.1)	$ 1.5	$ (0.2)