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, 2016		165.4
Balance at Dec. 31, 2016	$ 2,273.0	$ 165.4	$ 2,243.8	$ (510.0)	$ 373.8
Net (loss) income	549.5	0.0	0.0	0.0	549.5
Total other comprehensive (loss) income	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 (loss) income	327.9	0.0	0.0	0.0	327.9
Total other comprehensive (loss) income	(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
Lease accounting adoption adjustment	11.2	0.0	0.0	0.0	11.2
Net (loss) income	(11.3)	0.0	0.0	0.0	(11.3)
Total other comprehensive (loss) income	(152.4)	0.0	0.0	(152.4)	0.0
Dividends paid:
Common stock ($0.80 per share)	(129.3)	$ 0.0	0.0	0.0	(129.3)
Common stock repurchased and retired (in shares)		(8.0)
Common stock repurchased and retired	$ (145.9)	$ (8.0)	(137.9)	0.0	0.0
Common stock issued for:
Stock options exercised (in shares)	0.1	0.1
Stock options exercised	$ 1.7	$ 0.1	1.6	0.0	0.0
Other transactions (in shares)		0.3
Other transactions	3.1	$ 0.3	2.8	0.0	0.0
Stock-based compensation	8.2	$ 0.0	8.2	0.0	0.0
Balance (in shares) at Dec. 31, 2019		157.7
Balance at Dec. 31, 2019	$ 2,417.5	$ 157.7	$ 2,122.1	$ (803.4)	$ 941.1