Net Income Per Share - Reconciliation between Basic and Diluted Weighted Average Shares Outstanding (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Earnings Per Share [Abstract]
Net income	$ 175.9	$ 190.4	$ 235.5	$ 161.1	$ 145.2	$ 220.3	$ 601.8	$ 526.6
Net income attributable to unvested awarded performance stock	(2.6)			(2.9)			(9.4)	(10.1)
Net income attributable to common shares	$ 173.3			$ 158.2			$ 592.4	$ 516.5
Weighted average number of common shares outstanding – basic	284.1			283.0			283.7	282.7
Less unvested awarded performance stock included in weighted average number of common shares outstanding - basic	(4.2)			(5.2)			(4.4)	(5.4)
Weighted average number of common shares outstanding for basic net income per common share	279.9			277.8			279.3	277.3
Dilutive effect of potentially issuable common shares	1.4			0.9			1.1	1.2
Weighted average number of shares outstanding – diluted	281.3			278.7			280.4	278.5
Basic (in dollars per share)	$ 0.62			$ 0.57			$ 2.12	$ 1.86
Diluted (in dollars per share)	$ 0.62			$ 0.57			$ 2.11	$ 1.85