Consolidated Statements of Equity - USD ($) $ in Millions	Total	Total equity	Total common shareholders' equity	Common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income (loss)	Preferred stock of subsidiary	Noncontrolling interests
Balance at Dec. 31, 2017		$ 9,491.8	$ 9,461.4	$ 3.2	$ 4,278.5	$ 5,176.8	$ 2.9	$ 30.4	$ 0.0
Equity
Net income attributed to common shareholders	$ 1,059.3	1,059.3	1,059.3	0.0	0.0	1,059.3	0.0	0.0	0.0
Net income (loss) attributed to noncontrolling interests	0.0
Other comprehensive loss	(5.5)	(6.1)	(6.1)	0.0	0.0	0.0	(6.1)	0.0	0.0
Common stock dividends		(697.3)	(697.3)	0.0	0.0	(697.3)	0.0	0.0	0.0
Exercise of stock options		29.1	29.1	0.0	29.1	0.0	0.0	0.0	0.0
Purchase of common stock	(72.4)	(72.4)	(72.4)	0.0	(72.4)	0.0	0.0	0.0	0.0
Cumulative effect adjustment from ASU 2018-02 adoption		0.0	0.0	0.0	0.0	(0.6)	0.6	0.0	0.0
Acquisition of noncontrolling interests		23.8	0.0	0.0	0.0	0.0	0.0	0.0	23.8
Capital contributions from noncontrolling interest	0.0
Stock-based compensation and other		14.5	14.9	0.0	14.9	0.0	0.0	0.0	(0.4)
Balance at Dec. 31, 2018		9,842.7	9,788.9	3.2	4,250.1	5,538.2	(2.6)	30.4	23.4
Equity
Net income attributed to common shareholders	1,134.0	1,134.0	1,134.0	0.0	0.0	1,134.0	0.0	0.0	0.0
Net income (loss) attributed to noncontrolling interests	(0.5)	(0.5)	0.0	0.0	0.0	0.0	0.0	0.0	(0.5)
Other comprehensive loss	(1.5)	(1.5)	(1.5)	0.0	0.0	0.0	(1.5)	0.0	0.0
Common stock dividends		(744.5)	(744.5)	0.0	0.0	(744.5)	0.0	0.0	0.0
Exercise of stock options		67.0	67.0	0.0	67.0	0.0	0.0	0.0	0.0
Purchase of common stock	(140.1)	(140.1)	(140.1)	0.0	(140.1)	0.0	0.0	0.0	0.0
Acquisition of noncontrolling interests		69.0	0.0	0.0	0.0	0.0	0.0	0.0	69.0
Capital contributions from noncontrolling interest	21.0	21.0	0.0	0.0	0.0	0.0	0.0	0.0	21.0
Distributions to noncontrolling interests		(2.1)	0.0	0.0	0.0	0.0	0.0	0.0	(2.1)
Stock-based compensation and other		9.6	9.6	0.0	9.6	0.0	0.0	0.0	0.0
Balance at Dec. 31, 2019		10,254.6	10,113.4	3.2	4,186.6	5,927.7	(4.1)	30.4	110.8
Equity
Net income attributed to common shareholders	1,199.9	1,199.9	1,199.9	0.0	0.0	1,199.9	0.0	0.0	0.0
Net income (loss) attributed to noncontrolling interests	0.3	0.3	0.0	0.0	0.0	0.0	0.0	0.0	0.3
Other comprehensive loss	(2.7)	(2.7)	(2.7)	0.0	0.0	0.0	(2.7)	0.0	0.0
Common stock dividends		(798.0)	(798.0)	0.0	0.0	(798.0)	0.0	0.0	0.0
Exercise of stock options		43.8	43.8	0.0	43.8	0.0	0.0	0.0	0.0
Purchase of common stock	(99.2)	(99.2)	(99.2)	0.0	(99.2)	0.0	0.0	0.0	0.0
Purchase of additional ownership interest in Upstream from noncontrolling interest		(31.0)	0.0	0.0	0.0	0.0	0.0	0.0	(31.0)
Acquisition of noncontrolling interests		85.0	0.0	0.0	0.0	0.0	0.0	0.0	85.0
Capital contributions from noncontrolling interest	$ 0.0
Distributions to noncontrolling interests		(2.7)	0.0	0.0	0.0	0.0	0.0	0.0	(2.7)
Stock-based compensation and other		12.5	12.5	0.0	12.5	0.0	0.0	0.0	0.0
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