Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 188.2	$ 148.8
Accounts receivable, net	247.1	274.2
Materials and supplies	127.2	150.6
Other current assets	63.3	155.0
Total current assets	625.8	728.6
Operating lease right-of-use assets	70.9	158.4
Investments	42.6	47.6
Property and equipment (including concession assets), net	8,997.8	8,806.3
Other assets	226.9	45.9
Total assets	9,964.0	9,786.8
Current liabilities:
Long-term debt due within one year	6.4	18.0
Accounts payable and accrued liabilities	470.0	473.3
Total current liabilities	476.4	491.3
Long-term operating lease liabilities	45.4	85.7
Long-term debt	3,764.4	3,228.0
Deferred income taxes	1,185.4	1,128.0
Other noncurrent liabilities and deferred credits	108.8	107.9
Total liabilities	5,580.4	5,040.9
Stockholders’ equity:
$0.01 par, common stock, 400,000,000 shares authorized, 123,352,185 shares issued; 91,047,107 and 96,115,669 shares outstanding at December 31, 2020 and 2019, respectively	0.9	1.0
Additional paid-in capital	830.9	843.7
Retained earnings	3,219.6	3,601.3
Accumulated other comprehensive income (loss)	0.4	(29.1)
Total stockholders’ equity	4,057.2	4,422.5
Noncontrolling interest	326.4	323.4
Total equity	4,383.6	4,745.9
Total liabilities and equity	9,964.0	9,786.8
$25 Par Preferred Stock [Member]
Stockholders’ equity:
$25 par, 4% noncumulative, preferred stock, 840,000 shares authorized, 649,736 shares issued; 215,199 and 222,625 shares outstanding at December 31, 2020 and 2019, respectively	$ 5.4	$ 5.6