Contingencies and Commitments - Narrative (Detail) - USD ($) $ in Millions		1 Months Ended	9 Months Ended
	Mar. 20, 2022	Jun. 30, 2022	Sep. 30, 2022	Dec. 31, 2021
Business Acquisition [Line Items]
Total assets			$ 902,296	$ 958,784
Excess consideration paid for acquiring noncontrolling Interest		$ 362
Alleghany Corporation [Member]
Business Acquisition [Line Items]
Business acquisition, cash consideration	$ 11,600
Business acquisition, effective date of acquisition			Oct. 19, 2022
Business acquisition, agreement date			Mar. 20, 2022
Total assets			$ 31,200
Total liabilities			$ 23,400
Greg Abel | Berkshire Hathaway Energy [Member]
Business Acquisition [Line Items]
Acquisition of outstanding shares, value		$ 870