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Pension and Postretirement Plans (Narrative) (Details) - Defined Benefit Pension Plan [Member]
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2017
USD ($)
Investment
companies
Dec. 31, 2016
USD ($)
Investment
Retirement Benefits Disclosure [Line Items]    
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]    
Retirement Benefits Disclosure [Line Items]    
Defined benefit plan, target allocation maximum percentage of assets, equity securities 23.00%  
Fixed income securities [Member]    
Retirement Benefits Disclosure [Line Items]    
Defined benefit plan, target allocation percentage of assets, fixed-income securities, range minimum 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 | $ $ 990.9 $ 978.8
Percentage of total plan assets 47.00% 48.00%
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 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 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%