Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 470.0	$ 188.2
Accounts receivable, net	267.3	247.1
Materials and supplies	128.7	127.2
Other current assets	55.9	63.3
Total current assets	921.9	625.8
Operating lease right-of-use assets	69.3	70.9
Investments	54.6	42.6
Property and equipment (including concession assets), net	9,178.4	8,997.8
Other assets	318.6	226.9
Total assets	10,542.8	9,964.0
Current liabilities:
Long-term debt due within one year	8.7	6.4
Accounts payable and accrued liabilities	1,266.4	470.0
Total current liabilities	1,275.1	476.4
Long-term operating lease liabilities	45.9	45.4
Long-term debt	3,770.3	3,764.4
Deferred income taxes	1,067.8	1,185.4
Other noncurrent liabilities and deferred credits	150.9	108.8
Total liabilities	6,310.0	5,580.4
Stockholders' equity:
$.01 par, common stock, 400,000,000 shares authorized; 123,352,185 shares issued; 90,976,267 and 91,047,107 shares outstanding at September 30, 2021 and December 31, 2020, respectively	0.9	0.9
Additional paid-in capital	923.7	830.9
Retained earnings	2,929.9	3,219.6
Accumulated other comprehensive income	45.3	0.4
Total stockholders’ equity	3,905.2	4,057.2
Noncontrolling interest	327.6	326.4
Total equity	4,232.8	4,383.6
Total liabilities and equity	10,542.8	9,964.0
$25 Par Preferred Stock [Member]
Stockholders' equity:
$25 par, 4% noncumulative, preferred stock, 840,000 shares authorized, 649,736 shares issued; 214,542 and 215,199 shares outstanding at September 30, 2021 and December 31, 2020, respectively	$ 5.4	$ 5.4