Reinsurance - Effective Exit of GMDB and GMIB Business (Details) - Berkshire Hathway Life Insurance Company Of Nebraska [Member] - Variable Annuity [Member] - USD ($) $ in Billions	Dec. 31, 2017	Dec. 31, 2014
Ceded Credit Risk [Line Items]
Percent of future claim payments reinsured		100.00%
Ceded Reinsurance Agreement, Coverage Limit, Amount Remaining	$ 3.4