CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY (unaudited) - USD ($) $ in Millions	Total	Common stock	Additional paid-in capital	Retained earnings (deficit)	Accumulated other comprehensive loss
Beginning Balance at Dec. 31, 2016					$ (452.8)
Balance as adjusted at Dec. 31, 2016					(452.8)
Net income	$ 307.1
Other comprehensive income (loss), net of tax	60.6
Ending Balance at Sep. 30, 2017					(392.2)
Beginning Balance at Jun. 30, 2017					(425.7)
Balance as adjusted at Jun. 30, 2017					(425.7)
Net income	73.8
Other comprehensive income (loss), net of tax	33.5
Ending Balance at Sep. 30, 2017					(392.2)
Beginning Balance at Dec. 31, 2017	754.3	$ 1.2	$ 1,399.0	$ (267.2)	(378.7)
Change in accounting principle - ASU 2016-01 at Dec. 31, 2017				4.8	(4.8)
Balance as adjusted at Dec. 31, 2017	754.3	1.2	1,399.0	(262.4)	(383.5)
Net income	181.0			181.0
Other comprehensive income (loss), net of tax	(2.9)				(2.9)
Issuance of common stock	0.1		0.1
Dividends paid	(59.1)			(59.1)
Ending Balance at Sep. 30, 2018	873.4	1.2	1,399.1	(140.5)	(386.4)
Beginning Balance at Jun. 30, 2018					(393.3)
Balance as adjusted at Jun. 30, 2018					(393.3)
Net income	32.6
Other comprehensive income (loss), net of tax	6.9
Ending Balance at Sep. 30, 2018	$ 873.4	$ 1.2	$ 1,399.1	$ (140.5)	$ (386.4)