v3.19.3.a.u2
Investment in Cenovus Energy (Details) - USD ($)
$ / shares in Units, shares in Millions
 5 Months Ended 12 Months Ended
May 17, 2017
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]        
Investment in Cenovus Energy   $ 2,111,000,000 $ 1,462,000,000  
Unrealized Gain (Loss) on Securities, before tax [1]   649,000,000 (437,000,000) $ 0
Foster Creek Christina Lake (FCCL) [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Ownership percentage in equity investment 50.00%      
Common Stock [Member] | Cenovus Energy [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Shares Exchanged for Assets Held for Sale 208      
Percent of issued and outstanding common shares of Cenovus 16.90%      
Investment In Equity Security Fair Value $ 1,960,000,000 $ 2,110,000,000 $ 1,460,000,000  
Cenovus Energy common share price $ 9.41 $ 10.15    
Unrealized Gain (Loss) on Securities, before tax   $ 649,000,000    
[1]
*See Note 7—Investment in Cenovus Energy, for additional information.