Consolidated Statements of Changes in Equity - USD ($) $ in Millions	Total	Common Stock	Retained earnings	AOCI	Non-controlling interests
Beginning balance (in shares) at Dec. 31, 2018		255,326,252
Beginning balance at Dec. 31, 2018	$ 9,990.7	$ 8,685.2	$ 1,346.0	$ (3.0)	$ (37.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	103.4		99.5		3.9
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		60,594
Issuance of stock compensation and reinvested dividends, net of tax withholding	(1.6)	$ (1.6)
Dividends declared on common stock	(119.8)		(119.8)
Stock compensation expense	5.4	$ 5.4
Repurchase of common stock (in shares)		(10,548,060)
Repurchase of common stock	(578.3)	$ (578.3)
Consolidation of noncontrolling interests	3.8				3.8
Distributions to shareholders of noncontrolling interests	(1.4)				(1.4)
Derivative hedging activity, net of tax	(10.2)			(10.2)
Other	(0.3)	$ (0.3)
Ending balance (in shares) at Mar. 31, 2019		244,838,786
Ending balance at Mar. 31, 2019	9,391.7	$ 8,110.4	1,325.7	(13.2)	(31.2)
Beginning balance (in shares) at Dec. 31, 2018		255,326,252
Beginning balance at Dec. 31, 2018	9,990.7	$ 8,685.2	1,346.0	(3.0)	(37.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	248.0
Derivative hedging activity, net of tax	(26.0)
Change in unrecognized pension expense, net of tax	0.0
Ending balance (in shares) at Jun. 30, 2019		235,465,848
Ending balance at Jun. 30, 2019	8,854.7	$ 7,563.0	1,349.1	(29.0)	(28.4)
Beginning balance (in shares) at Mar. 31, 2019		244,838,786
Beginning balance at Mar. 31, 2019	9,391.7	$ 8,110.4	1,325.7	(13.2)	(31.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	144.6		139.7		4.9
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		41,982
Issuance of stock compensation and reinvested dividends, net of tax withholding	(0.7)	$ (0.7)
Dividends declared on common stock	(115.8)		(115.8)
Dividend equivalents declared	(0.5)		(0.5)
Stock compensation expense	$ 4.0	4.0
Repurchase of common stock (in shares)	(9,414,920)
Repurchase of common stock	$ (550.4)	(550.4)
Distributions to shareholders of noncontrolling interests	(2.1)				(2.1)
Derivative hedging activity, net of tax	(15.8)			(15.8)
Change in unrecognized pension expense, net of tax	0.0
Other	(0.3)	$ (0.3)
Ending balance (in shares) at Jun. 30, 2019		235,465,848
Ending balance at Jun. 30, 2019	8,854.7	$ 7,563.0	1,349.1	(29.0)	(28.4)
Beginning balance (in shares) at Dec. 31, 2019		226,641,443
Beginning balance at Dec. 31, 2019	8,545.3	$ 7,070.4	1,551.5	(50.0)	(26.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	72.2		69.4		2.8
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		97,305
Issuance of stock compensation and reinvested dividends, net of tax withholding	(3.0)	$ (3.0)
Dividends declared on common stock	(114.5)		(114.5)
Dividend equivalents declared	(0.7)		(0.7)
Stock compensation expense	4.6	4.6
Derivative hedging activity, net of tax	1.3			1.3
Other	0.2	$ 0.2
Ending balance (in shares) at Mar. 31, 2020		226,738,748
Ending balance at Mar. 31, 2020	8,505.4	$ 7,072.2	1,505.7	(48.7)	(23.8)
Beginning balance (in shares) at Dec. 31, 2019		226,641,443
Beginning balance at Dec. 31, 2019	8,545.3	$ 7,070.4	1,551.5	(50.0)	(26.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	208.5
Derivative hedging activity, net of tax	0.3
Change in unrecognized pension expense, net of tax	(0.1)
Ending balance (in shares) at Jun. 30, 2020		226,825,105
Ending balance at Jun. 30, 2020	8,526.9	$ 7,073.5	1,524.1	(49.8)	(20.9)
Beginning balance (in shares) at Mar. 31, 2020		226,738,748
Beginning balance at Mar. 31, 2020	8,505.4	$ 7,072.2	1,505.7	(48.7)	(23.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	136.3		133.4		2.9
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		86,357
Issuance of stock compensation and reinvested dividends, net of tax withholding	(2.9)	$ (2.9)
Dividends declared on common stock	(114.6)		(114.6)
Dividend equivalents declared	(0.4)		(0.4)
Stock compensation expense	4.1	4.1
Derivative hedging activity, net of tax	(1.0)			(1.0)
Change in unrecognized pension expense, net of tax	(0.1)			(0.1)
Other	0.1	$ 0.1
Ending balance (in shares) at Jun. 30, 2020		226,825,105
Ending balance at Jun. 30, 2020	$ 8,526.9	$ 7,073.5	$ 1,524.1	$ (49.8)	$ (20.9)