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			(27,500,000)
Dividends Declared [Table Text Block]	1.68
Balance at beginning of year at Dec. 31, 2016		67,000,000.0
Balance at beginning of period, Common Stock at Dec. 31, 2016		$ 41.5
Balance at beginning of period at Dec. 31, 2016			$ (999.0)	$ 687.8	$ 1,828.0	$ (211.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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
Dividends declared ($1.84 in 2019, $1.76 in 2018 and $1.68 in 2017)					68.2
Other comprehensive income (loss)	101.5
Balance at end of period, Common Stock, Shares at Dec. 31, 2017		67,100,000
Balance at end of period, Common Stock at Dec. 31, 2017		$ 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 | Retained Earnings [Member]	(0.1)
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			(29,200,000)
Dividends Declared [Table Text Block]	1.76
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 ($1.84 in 2019, $1.76 in 2018 and $1.68 in 2017)					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)
Dividends Declared [Table Text Block]	1.84
Issuance of common stock, Shares		200,000
Issuance of common stock		$ 0.2
Stock repurchases, Shares	2,000,000.0
Stock repurchases	$ (150.0)
Share-based compensation effects				13.7
Net income	211.2
Dividends declared ($1.84 in 2019, $1.76 in 2018 and $1.68 in 2017)					68.5
Other comprehensive income (loss)	$ 1.0
Balance at end of period, Common Stock, Shares at Dec. 31, 2019	67,500,000	67,500,000
Balance at end of period, Common Stock at Dec. 31, 2019	$ 41.8	$ 41.8
Balance at end of period at Dec. 31, 2019	1,835.1		$ (1,364.5)	$ 720.1	$ 2,601.3	$ (163.6)
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]	39.4
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			(32,700,000)