CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Retained Earnings
Balance (in shares) at Dec. 31, 2015		165.1
Balance at Dec. 31, 2015	$ 2,418.8	$ 165.1	$ 2,236.4	$ (492.5)	$ 509.8
Net income (loss)	(3.9)	0.0	0.0	0.0	(3.9)
Total other comprehensive (loss) income, net of tax	(17.5)	0.0	0.0	(17.5)	0.0
Dividends paid:
Common stock ($0.80 per share)	$ (132.1)	$ 0.0	0.0	0.0	(132.1)
Common stock issued for:
Stock options exercised (in shares)	0.3	0.3
Stock options exercised	$ 4.1	$ 0.3	3.8	0.0	0.0
Other transactions (in shares)		0.0
Other transactions	(0.8)	$ 0.0	(0.8)	0.0	0.0
Stock-based compensation	4.4	$ 0.0	4.4	0.0	0.0
Balance (in shares) at Dec. 31, 2016		165.4
Balance at Dec. 31, 2016	2,273.0	$ 165.4	2,243.8	(510.0)	373.8
Net income (loss)	549.5	0.0	0.0	0.0	549.5
Total other comprehensive (loss) income, net of tax	25.4	0.0	0.0	25.4	0.0
Dividends paid:
Common stock ($0.80 per share)	$ (133.0)	$ 0.0	0.0	0.0	(133.0)
Common stock issued for:
Stock options exercised (in shares)	1.7	1.7
Stock options exercised	$ 32.4	$ 1.7	30.7	0.0	0.0
Other transactions (in shares)		0.0
Other transactions	(0.9)	$ 0.0	(0.9)	0.0	0.0
Stock-based compensation	7.3	$ 0.0	7.3	0.0	0.0
Balance (in shares) at Dec. 31, 2017		167.1
Balance at Dec. 31, 2017	2,753.7	$ 167.1	2,280.9	(484.6)	790.3
Income tax reclassification adjustment	0.0	0.0	0.0	(85.9)	85.9
Net income (loss)	327.9	0.0	0.0	0.0	327.9
Total other comprehensive (loss) income, net of tax	(80.5)	0.0	0.0	(80.5)	0.0
Dividends paid:
Common stock ($0.80 per share)	(133.6)	$ 0.0	0.0	0.0	(133.6)
Common stock repurchased and retired (in shares)		(2.1)
Common stock repurchased and retired	$ (50.0)	$ (2.1)	(47.9)	0.0	0.0
Common stock issued for:
Stock options exercised (in shares)	0.2	0.2
Stock options exercised	$ 3.4	$ 0.2	3.2	0.0	0.0
Other transactions (in shares)		0.1
Other transactions	2.1	$ 0.1	2.0	0.0	0.0
Stock-based compensation	9.2	$ 0.0	9.2	0.0	0.0
Balance (in shares) at Dec. 31, 2018		165.3
Balance at Dec. 31, 2018	$ 2,832.2	$ 165.3	$ 2,247.4	$ (651.0)	$ 1,070.5