CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings Cumulative Effect, Period of Adoption, Adjusted Balance	Treasury Stock
Balance at Beginning of Year at Dec. 31, 2018		$ 30.5	$ 2,321.7	$ (814.2)	$ 9,863.1			$ (2,779.3)
Balance at Beginning of Year (Accounting Standards Update 2016-02) at Dec. 31, 2018						$ (3.4)	$ 9,859.7
Increase (Decrease) in Stockholders' Equity
Common Stock Activity		0.1	20.6
Other Comprehensive Income	$ 661.0			661.0
Net Income	804.1				804.1
Dividends to Stockholders (per common share: $0.285; $0.285; $0.855; $0.805)					(172.3)
Purchases of Treasury Stock								(300.3)
Balance at End of Year at Sep. 30, 2019	9,631.6	30.6	2,342.3	(153.2)	10,491.5			(3,079.6)
Balance at Beginning of Year at Jun. 30, 2019		30.6	2,335.6	(242.5)	10,308.9			(2,979.5)
Balance at Beginning of Year (Accounting Standards Update 2016-02) at Jun. 30, 2019						0.0	10,308.9
Increase (Decrease) in Stockholders' Equity
Common Stock Activity		0.0	6.7
Other Comprehensive Income	89.3			89.3
Net Income	242.0				242.0
Dividends to Stockholders (per common share: $0.285; $0.285; $0.855; $0.805)					(59.4)
Purchases of Treasury Stock								(100.1)
Balance at End of Year at Sep. 30, 2019	9,631.6	30.6	2,342.3	(153.2)	10,491.5			(3,079.6)
Balance at Beginning of Year at Dec. 31, 2019	9,965.0	30.6	2,348.1	37.3	10,728.7			(3,179.7)
Balance at Beginning of Year (Accounting Standards Update 2016-13) at Dec. 31, 2019						(18.9)	10,709.8
Increase (Decrease) in Stockholders' Equity
Common Stock Activity		0.1	23.2
Other Comprehensive Income	440.3			440.3
Net Income	657.6				657.6
Dividends to Stockholders (per common share: $0.285; $0.285; $0.855; $0.805)					(175.1)
Purchases of Treasury Stock								0.0
Balance at End of Year at Sep. 30, 2020	10,892.2	30.7	2,371.3	477.6	11,192.3			(3,179.7)
Balance at Beginning of Year at Jun. 30, 2020		30.6	2,364.1	327.2	11,019.2			(3,179.7)
Balance at Beginning of Year (Accounting Standards Update 2016-13) at Jun. 30, 2020						$ 0.0	$ 11,019.2
Increase (Decrease) in Stockholders' Equity
Common Stock Activity		0.1	7.2
Other Comprehensive Income	150.4			150.4
Net Income	231.1				231.1
Dividends to Stockholders (per common share: $0.285; $0.285; $0.855; $0.805)					(58.0)
Purchases of Treasury Stock								0.0
Balance at End of Year at Sep. 30, 2020	$ 10,892.2	$ 30.7	$ 2,371.3	$ 477.6	$ 11,192.3			$ (3,179.7)