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Investment gains/losses - Narrative (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Gain (Loss) on Investments [Line Items]        
Investment gains/losses $ 2,366 $ 492 $ 3,497 $ 997
Equity Securities [Member] | PSX and GHC [Member] | PSPI and WPLG Inc. [Member]
       
Gain (Loss) on Investments [Line Items]        
Investment gains/losses     2,100  
Equity Securities [Member] | Graham Holding Company [Member] | WPLG Inc. [Member]
       
Gain (Loss) on Investments [Line Items]        
Investment gains/losses $ 1,100