CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock	Restatement Adjustment Accumulated Other Comprehensive Income (Loss)	Restatement Adjustment Retained Earnings
Increase (Decrease) in Stockholders' Equity
Cumulative Effect of New Accounting Principle in Period of Adoption				$ (17.5)	$ 14.5
Balance at Beginning of Period at Dec. 31, 2017		$ 30.5	$ 2,303.3	127.5	9,542.2	$ (2,428.6)	$ 110.0	$ 9,556.7
Increase (Decrease) in Stockholders' Equity
Stock Issued During Period, Value, New Issues			(0.9)
Total Other Comprehensive Income (Loss)	$ (192.4)			(192.4)
Net Income	273.5				273.5
Dividends, Cash					52.4
Treasury Stock, Value, Acquired, Cost Method	(100.2)					(100.2)
Balance at End of Period at Mar. 31, 2018	9,499.5	30.5	2,302.4	(82.4)	9,777.8	(2,528.8)
Increase (Decrease) in Stockholders' Equity
Cumulative Effect of New Accounting Principle in Period of Adoption				0.0	(3.4)
Balance at Beginning of Period at Dec. 31, 2018	8,621.8	30.5	2,321.7	(814.2)	9,863.1	(2,779.3)	$ (814.2)	$ 9,859.7
Increase (Decrease) in Stockholders' Equity
Stock Issued During Period, Value, New Issues			6.8
Total Other Comprehensive Income (Loss)	311.9			311.9
Net Income	280.9				280.9
Dividends, Cash					57.5
Treasury Stock, Value, Acquired, Cost Method	(100.0)					(100.0)
Balance at End of Period at Mar. 31, 2019	$ 9,060.5	$ 30.5	$ 2,328.5	$ (502.3)	$ 10,083.1	$ (2,879.3)