Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
OPERATING ACTIVITIES
Net income	$ 701	$ 607
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	463	446
Deferred income taxes	137	196
Long-term casualty and environmental liabilities, net	(46)	(19)
Contributions to defined benefit pension plan	(36)	0
Other, net	(29)	(64)
Changes in current assets and liabilities:
Accounts receivable, net	47	(132)
Materials and supplies	(97)	(74)
Other current assets	(76)	(126)
Accounts payable and other current liabilities	15	(9)
Net cash provided by operating activities	1,079	825
INVESTING ACTIVITIES
Capital expenditures excluding equipment	(489)	(444)
Acquisition of equipment	(298)	(63)
Other, net	(169)	(95)
Net cash used for investing activities	(956)	(602)
FINANCING ACTIVITIES
Proceeds from issuance of long-term debt	1,250	0
Payments on long-term debt	(46)	(52)
Cash distributions	(1,000)	(1,000)
Other, net	(11)	0
Net cash provided by (used for) by financing activities	193	(1,052)
Increase (decrease) in cash and cash equivalents	316	(829)
Cash and cash equivalents:
Beginning of period	1,960	2,087
End of period	2,276	1,258
SUPPLEMENTAL CASH FLOW INFORMATION
Interest paid, net of amounts capitalized	189	187
Capital investments accrued but not yet paid	118	100
Income taxes paid, net of refunds	28	1
Non-cash asset financing	$ 0	$ 1