Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Millions	Total	Common stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			(24,800,000)
Balance at beginning of year at Dec. 31, 2015		66,800,000
Balance at beginning of period, Common Stock at Dec. 31, 2015		$ 41.5
Balance at beginning of period at Dec. 31, 2015			$ (878.9)	$ 677.4	$ 1,639.0	$ (198.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, Shares		200,000
Issuance of common stock		$ 0.0
Stock repurchases, Shares	2,700,000
Stock repurchases	$ (120.1)
Share-based compensation effects				10.4
Net income	257.1				257.1
Dividends declared					68.1
Other comprehensive income (loss)	(12.3)					(12.3)
Balance at end of period, Common Stock, Shares at Dec. 31, 2016		67,000,000
Balance at end of period, Common Stock at Dec. 31, 2016		$ 41.5
Balance at end of period at Dec. 31, 2016	1,347.2		$ (999.0)	687.8	1,828.0	(211.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	0.0
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification | Reclassification out of Accumulated Other Comprehensive Income [Domain]	$ 0.0
Balance at beginning of period, Shares			(27,500,000)
Issuance of common stock, Shares		100,000
Issuance of common stock		$ 0.1
Stock repurchases, Shares	1,700,000
Stock repurchases	$ (100.0)
Share-based compensation effects				10.0
Net income	502.0				502.0
Dividends declared					68.2
Other comprehensive income (loss)	$ 101.5					101.5
Balance at end of period, Common Stock, Shares at Dec. 31, 2017	67,083,149	67,100,000
Balance at end of period, Common Stock at Dec. 31, 2017	$ 41.6	$ 41.6
Balance at end of period at Dec. 31, 2017	1,792.7		$ (1,099.0)	698.0	2,261.7	(109.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	0.2
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification | Reclassification out of Accumulated Other Comprehensive Income [Domain]	$ (0.1)
Balance at beginning of period, Shares			(29,200,000)
Issuance of common stock, Shares		200,000
Issuance of common stock		$ 0.0
Stock repurchases, Shares	1,500,000
Stock repurchases	$ (115.5)
Share-based compensation effects				8.4
Net income	211.3
Dividends declared					69.0
Other comprehensive income (loss)	$ (35.6)
Balance at end of period, Common Stock, Shares at Dec. 31, 2018	67,329,081	67,300,000
Balance at end of period, Common Stock at Dec. 31, 2018	$ 41.6	$ 41.6
Balance at end of period at Dec. 31, 2018	1,788.1		$ (1,214.5)	$ 706.4	$ 2,419.2	$ (164.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	0.0
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification | Retained Earnings [Member]	15.2
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification | Reclassification out of Accumulated Other Comprehensive Income [Domain]	$ (19.4)
Balance at beginning of period, Shares			(30,700,000)