Consolidated Statements of Changes in Shareholders' Equity (USD $) In Millions, except Share data, unless otherwise specified	Total	Common stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at beginning of period at Dec. 31, 2010
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			(19,100,000)
Other comprehensive income (loss)						$ 24.5
Balance at end of period at Dec. 31, 2011			(560.3)	644.4	1,171.2	(169.1)
Balance at beginning of period, Common Stock at Dec. 31, 2011		41.1
Balance at beginning of year at Dec. 31, 2011		65,800,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			(19,100,000)
Issuance of common stock, Shares		200,000
Issuance of common stock		0.1		2.9
Stock repurchases, Shares	0
Stock repurchases	0
Share-based compensation effects				11.2
Net income	137.3				137.3
Dividends declared					(59.1)
Other comprehensive income (loss)	24.5
Balance at end of period at Dec. 31, 2012	1,244.2		(560.3)	658.5	1,249.4	(144.6)
Balance at end of period, Common Stock at Dec. 31, 2012		41.2
Balance at end of period, Common Stock, Shares at Dec. 31, 2012		66,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			(20,500,000)
Issuance of common stock, Shares		300,000
Issuance of common stock		0.1		1.1
Stock repurchases, Shares	1,400,000
Stock repurchases	(68.6)
Share-based compensation effects				9.3
Net income	169.3				169.3
Dividends declared					(60.3)
Other comprehensive income (loss)	101.9					101.9
Balance at end of period at Dec. 31, 2013	1,397.0		(628.9)	668.9	1,358.4	(42.7)
Balance at end of period, Common Stock at Dec. 31, 2013	41.3	41.3
Balance at end of period, Common Stock, Shares at Dec. 31, 2013	66,349,906	66,300,000
Balance at beginning of period at Sep. 30, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			(20,500,000)
Net income	53.3
Balance at end of period at Dec. 31, 2013	1,397.0		(628.9)	668.9	1,358.4
Balance at end of period, Common Stock at Dec. 31, 2013	41.3	41.3
Balance at end of period, Common Stock, Shares at Dec. 31, 2013	66,349,906	66,300,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			(22,400,000)
Issuance of common stock, Shares		300,000
Issuance of common stock		0.1		0
Stock repurchases, Shares	1,900,000
Stock repurchases	(124.6)
Share-based compensation effects				3.9
Net income	205.0
Dividends declared					(61.7)
Other comprehensive income (loss)	(105.7)
Balance at end of period at Dec. 31, 2014	1,314.0		(753.5)	672.8	1,501.7	(148.4)
Balance at end of period, Common Stock at Dec. 31, 2014	41.4	41.4
Balance at end of period, Common Stock, Shares at Dec. 31, 2014	66,600,984	66,600,000
Balance at beginning of period at Sep. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			(22,400,000)
Net income	58.5
Balance at end of period at Dec. 31, 2014	1,314.0		(753.5)			(148.4)
Balance at end of period, Common Stock at Dec. 31, 2014	$ 41.4
Balance at end of period, Common Stock, Shares at Dec. 31, 2014	66,600,984