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, 2020		226,836,670
Beginning balance at Dec. 31, 2020	$ 8,718.5	$ 7,080.0	$ 1,702.8	$ (49.4)	$ (14.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	194.6		191.6		3.0
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		104,896
Issuance of stock compensation and reinvested dividends, net of tax withholding	(1.1)	$ (1.1)
Issuance of restricted common stock (in shares)		54,054
Issuance of restricted common stock	2.9	$ 2.9
Dividends declared on common stock	(121.4)		(121.4)
Dividend equivalents declared	(0.2)		(0.2)
Stock compensation expense	2.6	2.6
Unearned compensation
Issuance of restricted common stock	(2.9)	(2.9)
Compensation expense recognized	0.4	0.4
Derivative hedging activity, net of tax	1.4			1.4
Other	(0.4)	$ (0.4)
Ending balance (in shares) at Mar. 31, 2021		226,995,620
Ending balance at Mar. 31, 2021	8,794.4	$ 7,081.5	1,772.8	(48.0)	(11.9)
Beginning balance (in shares) at Dec. 31, 2020		226,836,670
Beginning balance at Dec. 31, 2020	8,718.5	$ 7,080.0	1,702.8	(49.4)	(14.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	835.4
Unearned compensation
Derivative hedging activity, net of tax	4.1
Change in unrecognized pension expense, net of tax	0.0
Ending balance (in shares) at Sep. 30, 2021		229,301,079
Ending balance at Sep. 30, 2021	9,312.0	$ 7,201.8	2,161.3	(45.3)	(5.8)
Beginning balance (in shares) at Mar. 31, 2021		226,995,620
Beginning balance at Mar. 31, 2021	8,794.4	$ 7,081.5	1,772.8	(48.0)	(11.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	188.3		185.3		3.0
Issuance of stock, net of issuance costs (in shares)		2,269,447
Issuance of stock, net of issuance costs	112.5	$ 112.5
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		31,147
Issuance of stock compensation and reinvested dividends, net of tax withholding	(0.6)	$ (0.6)
Dividends declared on common stock	(122.6)		(122.6)
Dividend equivalents declared	(0.5)		(0.5)
Stock compensation expense	3.8	3.8
Unearned compensation
Compensation expense recognized	0.5	0.5
Derivative hedging activity, net of tax	1.4			1.4
Other	(0.1)	$ (0.1)
Ending balance (in shares) at Jun. 30, 2021		229,296,214
Ending balance at Jun. 30, 2021	8,977.1	$ 7,197.6	1,835.0	(46.6)	(8.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	452.5		449.4		3.1
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		4,865
Issuance of stock compensation and reinvested dividends, net of tax withholding	0.0
Dividends declared on common stock	(122.7)		(122.7)
Dividend equivalents declared	(0.4)		(0.4)
Stock compensation expense	3.6	$ 3.6
Unearned compensation
Compensation expense recognized	0.4	0.4
Derivative hedging activity, net of tax	1.3			1.3
Change in unrecognized pension expense, net of tax	0.0
Other	0.2	$ 0.2
Ending balance (in shares) at Sep. 30, 2021		229,301,079
Ending balance at Sep. 30, 2021	9,312.0	$ 7,201.8	2,161.3	(45.3)	(5.8)
Beginning balance (in shares) at Dec. 31, 2021		229,299,900
Beginning balance at Dec. 31, 2021	9,241.7	$ 7,205.5	2,082.9	(44.0)	(2.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	125.6		122.5		3.1
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		176,658
Issuance of stock compensation and reinvested dividends, net of tax withholding	(4.0)	$ (4.0)
Dividends declared on common stock	(131.3)		(131.3)
Dividend equivalents declared	(0.8)		(0.8)
Stock compensation expense	4.3	4.3
Unearned compensation
Compensation expense recognized	0.2	0.2
Derivative hedging activity, net of tax	1.4			1.4
Other	0.4	$ 0.4
Ending balance (in shares) at Mar. 31, 2022		229,476,558
Ending balance at Mar. 31, 2022	9,237.5	$ 7,206.4	2,073.3	(42.6)	0.4
Beginning balance (in shares) at Dec. 31, 2021		229,299,900
Beginning balance at Dec. 31, 2021	9,241.7	$ 7,205.5	2,082.9	(44.0)	(2.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	754.4
Unearned compensation
Derivative hedging activity, net of tax	4.1
Change in unrecognized pension expense, net of tax	0.1
Ending balance (in shares) at Sep. 30, 2022		229,532,136
Ending balance at Sep. 30, 2022	9,615.5	$ 7,216.6	2,432.2	(39.8)	6.5
Beginning balance (in shares) at Mar. 31, 2022		229,476,558
Beginning balance at Mar. 31, 2022	9,237.5	$ 7,206.4	2,073.3	(42.6)	0.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	197.6		194.5		3.1
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		38,743
Issuance of stock compensation and reinvested dividends, net of tax withholding	(0.3)	$ (0.3)
Dividends declared on common stock	(131.4)		(131.4)
Dividend equivalents declared	(0.4)		(0.4)
Stock compensation expense	6.3	6.3
Unearned compensation
Compensation expense recognized	0.2	0.2
Derivative hedging activity, net of tax	1.3			1.3
Change in unrecognized pension expense, net of tax	0.1			0.1
Other	(0.1)	$ (0.1)
Ending balance (in shares) at Jun. 30, 2022		229,515,301
Ending balance at Jun. 30, 2022	9,310.8	$ 7,212.5	2,136.0	(41.2)	3.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	431.2		428.2		3.0
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		16,835
Issuance of stock compensation and reinvested dividends, net of tax withholding	(0.2)	$ (0.2)
Dividends declared on common stock	(131.4)		(131.4)
Dividend equivalents declared	(0.6)		(0.6)
Stock compensation expense	4.0	4.0
Unearned compensation
Compensation expense recognized	0.2	0.2
Derivative hedging activity, net of tax	1.4			1.4
Change in unrecognized pension expense, net of tax	0.0
Other	0.1	$ 0.1
Ending balance (in shares) at Sep. 30, 2022		229,532,136
Ending balance at Sep. 30, 2022	$ 9,615.5	$ 7,216.6	$ 2,432.2	$ (39.8)	$ 6.5