Derivative contracts (Tables)
12 Months Ended
Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]  
Derivative contracts outstanding

The liabilities and related notional values of these contracts follows (in millions).

 

     Liabilities      Notional
Value
 

December 31, 2018

    $   2,452       $     26,759    

December 31, 2017

     2,172        28,753