Stock Incentive Plans (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2011
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	8,000
Status of Stock Options
Number of shares authorized for grant	7,000
Shares outstanding under option, beginning balance	1,714	1,997	2,872
Shares exercised	(440)	(283)	(870)
Shares forfeited	(7)		(5)
Shares outstanding under option, ending balance	1,267	1,714	1,997
Weighted average exercise price, beginning balance	$ 16.11	$ 15.82	$ 15.33
Weighted average exercise price, exercised	14.76	14.04	14.17
Weighted average exercise price, ending balance	16.59	$ 16.11	15.82
Weighted average exercise price, forfeited	$ 14.52		$ 17.48
Weighted average remaining contractual life outstanding, beginning balance		1 year 8 months	2 years 7 months	3 years 5 months
Aggregate intrinsic value, outstanding, beginning balance	$ 66.5	$ 80.0	$ 58.8
Aggregate intrinsic value, exercised	19.2	13.8	25.5
Aggregate intrinsic value, outstanding, ending balance	$ 33.7	66.5	80.0
Weighted average remaining contractual life, outstanding	11 months
Share under option, option exercisable	1,267
Weighted average exercise price, options exercisable	$ 16.59
Weighted average remaining contractual life option exercisable	11 months
Aggregate intrinsic value, option exercisable	$ 33.7
Proceeds from stock based compensation - gross	6.5	4.0	12.3
Tax benefit (loss)	10.3	12.9	20.7
Proceeds from stock options exercised, including the tax benefit	$ 16.8	$ 16.9	$ 33.0