Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
OPERATING ACTIVITIES
Net income	$ 1,682	$ 1,503
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	972	933
Deferred income taxes	295	290
Long-term casualty and environmental liabilities, net	(13)	(66)
Contribution to defined benefit pension plan	(25)	(36)
Other, net	(90)	(116)
Changes in current assets and liabilities:
Accounts receivable, net	(111)	24
Materials and supplies	(5)	(38)
Other current assets	(112)	(104)
Accounts payable and other current liabilities	(422)	(83)
Net cash provided by operating activities	2,171	2,307
INVESTING ACTIVITIES
Capital expenditures excluding equipment	(1,304)	(1,249)
Acquisition of equipment	(369)	(564)
Other, net	3	(126)
Net cash used for investing activities	(1,670)	(1,939)
FINANCING ACTIVITIES
Proceeds from issuance of long-term debt	1,500	1,250
Payments on long-term debt	(111)	(98)
Cash distributions	(2,000)	(1,750)
Other, net	(12)	(12)
Net cash used for financing activities	(623)	(610)
Decrease in cash and cash equivalents	(122)	(242)
Cash and cash equivalents:
Beginning of period	1,794	1,960
End of period	1,672	1,718
SUPPLEMENTAL CASH FLOW INFORMATION
Interest paid, net of amounts capitalized	375	341
Capital investments accrued but not yet paid	147	143
Income taxes paid, net of refunds	$ 1,042	$ 503