Pension plans - Projected benefit obligation, plan assets and net funded status (Detail) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Benefit obligations
Accumulated benefit obligation end of year	$ 17,524	$ 16,699
PBO beginning of year	17,750	15,259
Service cost	273	282	$ 266
Interest cost	635	691	591
Benefits paid	(897)	(1,014)
Business acquisitions		2,684
Actuarial (gains) or losses and other	1,063	(152)
PBO end of year	18,824	17,750	15,259
Plan assets
Plan assets beginning of year	15,397	12,831
Employer contributions	281	347
Benefits paid	(897)	(1,014)
Actual return on plan assets	2,136	1,595
Business acquisitions		2,314
Other	97	(676)
Plan assets end of year	17,014	15,397	12,831
Funded status - net liability	1,810	2,353
Berkshire Hathaway Energy [Member]
Benefit obligations
Accumulated benefit obligation end of year	4,920	4,787
PBO beginning of year	5,077	5,076
Service cost	47	49
Interest cost	174	198
Benefits paid	(271)	(309)
Actuarial (gains) or losses and other	180	63
PBO end of year	5,207	5,077	5,076
Plan assets
Plan assets beginning of year	4,694	4,765
Employer contributions	122	133
Benefits paid	(271)	(309)
Actual return on plan assets	535	512
Other	49	(407)
Plan assets end of year	5,129	4,694	4,765
Funded status - net liability	78	383
All Other [Member]
Benefit obligations
Accumulated benefit obligation end of year	12,604	11,912
PBO beginning of year	12,673	10,183
Service cost	226	233
Interest cost	461	493
Benefits paid	(626)	(705)
Business acquisitions		2,684
Actuarial (gains) or losses and other	883	(215)
PBO end of year	13,617	12,673	10,183
Plan assets
Plan assets beginning of year	10,703	8,066
Employer contributions	159	214
Benefits paid	(626)	(705)
Actual return on plan assets	1,601	1,083
Business acquisitions		2,314
Other	48	(269)
Plan assets end of year	11,885	10,703	$ 8,066
Funded status - net liability	$ 1,732	$ 1,970