Significant Business Acquisitions - Narrative (Detail) (USD $)	12 Months Ended	43 Months Ended				1 Months Ended	3 Months Ended	1 Months Ended
	Dec. 31, 2010	Feb. 11, 2010	Feb. 12, 2010	Sep. 16, 2011 The Lubrizol Corporation [Member]	Mar. 13, 2011 The Lubrizol Corporation [Member]	Dec. 31, 2010 Marmon Holdings [Member]	Mar. 31, 2011 Marmon Holdings [Member]	Jun. 30, 2011 Wesco Financial Corporation [Member]	Jun. 30, 2011 Wesco Financial Corporation [Member] Class B [Member]	Feb. 12, 2010 BNSF [Member]	Feb. 12, 2010 BNSF [Member] Class B [Member]	Feb. 12, 2010 BNSF [Member] Class A [Member]
Business Acquisition [Line Items]
Acquisition of remaining common stock outstanding, shares										264,500,000
Acquisition of common stock outstanding, dollars per share					$ 135
Acquisition of common stock outstanding, percentage							16.60%			77.50%
Aggregate consideration for acquisition of common stock outstanding, amount										$ 26,500,000,000
Aggregate consideration to acquire noncontrolling interest							1,500,000,000	543,000,000
Percentage of shares owned after stock transaction		22.50%					80.20%
Excess of the consideration paid over the carrying value of noncontrolling interest acquired						(614,000,000)
Acquisition paid in cash				8,704,000,000				298,000,000		15,900,000,000
Acquisition paid in common stock, shares									3,253,472		20,976,621	80,931
Shares owned prior to acquisition, shares		76,800,000
Equity method investment carrying value prior to investment in subsidiaries			6,600,000,000
Holding gain recognized for the difference between the fair value and carrying value of shares held under the equity method	$ 979,000,000