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Pension and Postretirement Plans (Narrative) (Details) - Defined Benefit Pension Plan [Member]
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2018
USD ($)
Investment
companies
Mar. 31, 2017
USD ($)
Dec. 31, 2017
USD ($)
Investment
Retirement Benefits Disclosure [Line Items]      
Curtailment gain | $ $ 806 $ 0  
Percent of plan assets managed internally by the company 45.00%    
Percent of plan assets managed by investment companies 55.00%    
Number of investment companies actively managing plan assets | companies 2    
Percentage of total plan assets 100.00%   100.00%
Berkshire Hathaway Common Stock [Member]      
Retirement Benefits Disclosure [Line Items]      
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator 20.00%    
Foreign Investments [Member] | Maximum [Member]      
Retirement Benefits Disclosure [Line Items]      
Defined benefit plan, target allocation percentage of assets 23.00%    
Fixed income securities [Member] | Minimum [Member]      
Retirement Benefits Disclosure [Line Items]      
Defined benefit plan, target allocation percentage of assets 10.00%    
Single Equity Concentration [Member]      
Retirement Benefits Disclosure [Line Items]      
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator 10.00%    
Value of investments | $ $ 1,052,800   $ 1,079,300
Percentage of total plan assets 45.00%   46.00%
Single Equity Concentration [Member] | Equity Securities [Member]      
Retirement Benefits Disclosure [Line Items]      
Number of investments the company's pension plan held which individually exceed 10% of total plan assets | Investment 1   1
Single Equity Concentration [Member] | Equity Funds [Member]      
Retirement Benefits Disclosure [Line Items]      
Number of investments the company's pension plan held which individually exceed 10% of total plan assets | Investment 1   1
Concentration In Single Entity, Type Of Industry, Foreign Country Or Individual Fund [Member] | Defined Benefit Plan Assets Total [Member]      
Retirement Benefits Disclosure [Line Items]      
Minimum percentage of plan assets considered as significant concentrations in pension plans 10.00%   10.00%