Significant business acquisitions - Narrative (Detail) (USD $)	9 Months Ended	12 Months Ended	0 Months Ended			0 Months Ended		9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Dec. 19, 2013 NV Energy [Member] Berkshire Hathaway Energy [Member]	Jan. 01, 2014 IMI plc Beverage Dispensing Equipment Manufacturing and Merchandising Operations [Member]	Feb. 25, 2014 Lubrizol Specialty Products Inc. (formerly Phillips Specialty Products Inc.) [Member]	Feb. 25, 2014 Lubrizol Specialty Products Inc. (formerly Phillips Specialty Products Inc.) [Member] PSX [Member]	Jun. 30, 2014 WPLG Inc. [Member] Graham Holding Company [Member]	Sep. 30, 2014 IMI plc, Lubrizol Specialty Products Inc. and WPLG Inc.[Member]
Business Acquisition [Line Items]
Aggregate consideration paid for acquisitions			$ 5,600,000,000	$ 1,120,000,000
Percentage of acquiree's common stock acquired					100.00%
Number of shares exchanged						17,422,615	1,620,190
Fair value of shares exchanged	2,478,000,000					1,350,000,000	1,130,000,000
Preliminary fair value of identified net assets								2,300,000,000
Residual goodwill	$ 1,818,000,000	$ 2,732,000,000						$ 1,300,000,000