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			(20,500,000)
Balance at beginning of year at Dec. 31, 2013		66,300,000
Balance at beginning of period, Common Stock at Dec. 31, 2013		$ 41.3
Balance at beginning of period at Dec. 31, 2013			$ (628.9)	$ 668.9	$ 1,358.4	$ (42.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, Shares		300,000
Issuance of common stock		$ 0.1		0.0
Stock repurchases, Shares	(1,900,000)
Stock repurchases	$ (124.6)
Share-based compensation effects				3.9
Net income	205.0				205.0
Dividends declared					(61.7)
Other comprehensive income (loss)	(105.7)
Balance at end of period, Common Stock, Shares at Dec. 31, 2014		66,600,000
Balance at end of period, Common Stock at Dec. 31, 2014		$ 41.4
Balance at end of period at Dec. 31, 2014	$ 1,314.0		$ (753.5)	672.8	1,501.7	(148.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			(22,400,000)
Issuance of common stock, Shares		200,000
Issuance of common stock		$ 0.1		0.0
Stock repurchases, Shares	(2,400,000)
Stock repurchases	$ (125.4)
Share-based compensation effects				4.6
Net income	205.3				205.3
Dividends declared					(68.0)
Other comprehensive income (loss)	$ (50.4)					(50.4)
Balance at end of period, Common Stock, Shares at Dec. 31, 2015	66,776,290	66,800,000
Balance at end of period, Common Stock at Dec. 31, 2015	$ 41.5	$ 41.5
Balance at end of period at Dec. 31, 2015	$ 1,280.2		$ (878.9)	677.4	1,639.0	(198.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			(24,800,000)
Issuance of common stock, Shares		200,000
Issuance of common stock		$ 0.0		0.0
Stock repurchases, Shares	(2,700,000)
Stock repurchases	$ (120.1)
Share-based compensation effects				10.4
Net income	257.1
Other comprehensive income (loss)	$ (12.3)
Balance at end of period, Common Stock, Shares at Dec. 31, 2016	66,953,606	67,000,000
Balance at end of period, Common Stock at Dec. 31, 2016	$ 41.5	$ 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]
Balance at beginning of period, Shares			(27,500,000)