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Dispositions - Canadian Business - Discontinued Operations (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
May 31, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Impairments       $ 24 $ 75 $ 229
Net gain on disposal of assets       $ 50 $ 319 58
Canadian Business [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Impairments     $ 6,600      
Impairments, after-tax     $ 4,960      
Canadian Business [Member] | Discontinued Operations, Disposed of by Sale [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Consideration received $ 2,500          
Disposal of assets, net of cash transferred to the buyer $ 1,800          
Impairments           $ 6,636
Net gain on disposal of assets   $ (43)        
Variable Interest Entity, Not Primary Beneficiary [Member] | Canadian Business [Member] | Discontinued Operations, Disposed of by Sale [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Interest in business 20.00%          
Notes Receivable [Member] | Canadian Business [Member] | Discontinued Operations, Disposed of by Sale [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Notes receivables received $ 750