CONDENSED CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Millions	Total	Total common shareholders' equity	Common stock	Additional paid in capital	Retained earnings	Accumulated other comprehensive loss	Preferred stock of subsidiary	Noncontrolling interests
Balance at Dec. 31, 2020	$ 10,662.5	$ 10,469.7	$ 3.2	$ 4,143.7	$ 6,329.6	$ (6.8)	$ 30.4	$ 162.4
Statements of equity
Net income attributed to common shareholders	510.1	510.1	0.0	0.0	510.1	0.0	0.0	0.0
Net income (loss) attributable to noncontrolling interests	(0.1)	0.0	0.0	0.0	0.0	0.0	0.0	(0.1)
Other comprehensive income	1.1	1.1	0.0	0.0	0.0	1.1	0.0	0.0
Common stock dividends	(213.7)	(213.7)	0.0	0.0	(213.7)	0.0	0.0	0.0
Exercise of stock options	1.2	1.2	0.0	1.2	0.0	0.0	0.0	0.0
Purchase of common stock	(6.6)	(6.6)	0.0	(6.6)	0.0	0.0	0.0	0.0
Acquisition of a noncontrolling interest	6.2	0.0	0.0	0.0	0.0	0.0	0.0	6.2
Capital contributions from noncontrolling interest	2.0	0.0	0.0	0.0	0.0	0.0	0.0	2.0
Distributions to noncontrolling interests	(0.4)	0.0	0.0	0.0	0.0	0.0	0.0	(0.4)
Stock-based compensation and other	5.3	5.3	0.0	5.3	0.0	0.0	0.0	0.0
Balance at Mar. 31, 2021	10,967.6	10,767.1	3.2	4,143.6	6,626.0	(5.7)	30.4	170.1
Balance at Dec. 31, 2021	11,113.3	10,913.2	3.2	4,138.1	6,775.1	(3.2)	30.4	169.7
Statements of equity
Net income attributed to common shareholders	565.9	565.9	0.0	0.0	565.9	0.0	0.0	0.0
Net income (loss) attributable to noncontrolling interests	1.8	0.0	0.0	0.0	0.0	0.0	0.0	1.8
Other comprehensive income	0.0
Common stock dividends	(229.6)	(229.6)	0.0	0.0	(229.6)	0.0	0.0	0.0
Exercise of stock options	11.8	11.8	0.0	11.8	0.0	0.0	0.0	0.0
Purchase of common stock	(23.4)	(23.4)	0.0	(23.4)	0.0	0.0	0.0	0.0
Capital contributions from noncontrolling interest	0.4	0.0	0.0	0.0	0.0	0.0	0.0	0.4
Distributions to noncontrolling interests	(1.0)	0.0	0.0	0.0	0.0	0.0	0.0	(1.0)
Stock-based compensation and other	5.3	5.3	0.0	5.3	0.0	0.0	0.0	0.0
Balance at Mar. 31, 2022	$ 11,444.5	$ 11,243.2	$ 3.2	$ 4,131.8	$ 7,111.4	$ (3.2)	$ 30.4	$ 170.9