Significant business acquisitions - Narrative (Detail) (USD $)			3 Months Ended	1 Months Ended
	Sep. 30, 2012	Sep. 16, 2011 The Lubrizol Corporation [Member]	Mar. 31, 2011 Marmon Holdings [Member]	Jun. 30, 2011 Wesco Financial Corporation [Member]	Jun. 30, 2011 Wesco Financial Corporation [Member] Class B [Member]
Business Acquisition [Line Items]
Aggregate consideration paid for acquisitions	$ 1,800,000,000
Acquisition of common stock outstanding, dollars per share		$ 135
Acquisition paid in cash		8,700,000,000		298,000,000
Percentage of shares owned after stock transactions			80.20%
Acquisition of common stock outstanding, percentage			16.60%
Aggregate consideration to acquire noncontrolling interest			$ 1,500,000,000	$ 543,000,000
Number of shares issued as consideration to acquire an entity					3,253,472