Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 72.6	$ 72.4
Accounts receivable, net	183.6	166.0
Materials and supplies	125.6	109.6
Deferred income taxes	92.1	225.0
Other current assets	48.4	69.5
Total current assets	522.3	642.5
Investments	51.5	50.4
Restricted funds	14.2	21.7
Property and equipment (including concession assets), net	5,684.8	5,321.6
Other assets	123.1	108.9
Total assets	6,395.9	6,145.1
Current liabilities:
Debt due within one year	60.2	36.3
Accounts payable and accrued liabilities	364.6	401.1
Total current liabilities	424.8	437.4
Long-term debt	1,547.6	1,602.8
Deferred income taxes	894.2	861.4
Other noncurrent liabilities and deferred credits	128.6	184.8
Total liabilities	2,995.2	3,086.4
Commitments and contingencies	0	0
Stockholders’ equity:
$.01 par, common stock, 400,000,000 shares authorized, 123,352,185 shares issued; 110,131,353 and 109,910,857 shares outstanding at December 31, 2012 and 2011, respectively	1.1	1.1
Paid-in capital	925.3	884.2
Retained earnings	2,166.5	1,875.3
Accumulated other comprehensive loss	(2.4)	(2.2)
Total stockholders’ equity	3,096.6	2,764.5
Noncontrolling interest	304.1	294.2
Total equity	3,400.7	3,058.7
Total liabilities and equity	6,395.9	6,145.1
$25 Par Preferred Stock [Member]
Stockholders’ equity:
$25 par, 4% noncumulative, preferred stock, 840,000 shares authorized, 649,736 shares issued, 242,170 shares outstanding	$ 6.1	$ 6.1