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, 2020	Dec. 31, 2019	Dec. 31, 2018
Benefit obligations
PBO beginning of year	$ 18,706	$ 16,922
Service cost	235	224	$ 271
Interest cost	510	618	593
Benefits paid	(994)	(1,033)
Settlements	(75)	(167)
Actuarial (gains) or losses and other	2,047	2,142
PBO end of year	20,429	18,706	16,922
Plan assets
Plan assets beginning of year	16,496	14,959
Employer contributions	196	199
Benefits paid	(994)	(1,033)
Actual return on plan assets	2,374	2,414
Settlements	(75)	(167)
Other	(59)	124
Plan assets end of year	17,938	16,496	14,959
Funded status – net liability	2,491	2,210
Berkshire Hathaway Energy [Member]
Benefit obligations
PBO beginning of year	4,898	4,551
Service cost	33	32
Interest cost	133	161
Benefits paid	(285)	(257)
Settlements	(63)	(121)
Actuarial (gains) or losses and other	566	532
PBO end of year	5,282	4,898	4,551
Plan assets
Plan assets beginning of year	4,808	4,385
Employer contributions	69	68
Benefits paid	(285)	(257)
Actual return on plan assets	554	650
Settlements	(63)	(121)
Other	75	83
Plan assets end of year	5,158	4,808	4,385
Funded status – net liability	124	90
Other [Member]
Benefit obligations
PBO beginning of year	13,808	12,371
Service cost	202	192
Interest cost	377	457
Benefits paid	(709)	(776)
Settlements	(12)	(46)
Actuarial (gains) or losses and other	1,481	1,610
PBO end of year	15,147	13,808	12,371
Plan assets
Plan assets beginning of year	11,688	10,574
Employer contributions	127	131
Benefits paid	(709)	(776)
Actual return on plan assets	1,820	1,764
Settlements	(12)	(46)
Other	(134)	41
Plan assets end of year	12,780	11,688	$ 10,574
Funded status – net liability	$ 2,367	$ 2,120