Supplemental cash flow information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 2,885	$ 3,547	$ 2,032
Non-cash investing activity - liabilities assumed in connection with acquisitions	5,836	31,406	278
BNSF [Member]
Supplemental Cash Flow Information [Line Items]
Non-cash investing activity - common stock issued in connection with acquisition		10,577
Wesco Financial Corporation [Member]
Supplemental Cash Flow Information [Line Items]
Non-cash financing activity - common stock issued in connection with acquisition of noncontrolling interests	245
Insurance and Other [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	243	185	145
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	1,821	1,667	1,142
Finance and Financial Products [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 662	$ 708	$ 615