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Summary of Significant Accounting Policies - Property, plant and equipment and depreciation (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Property, plant and equipment and depreciation      
Depreciation expense $ 191 $ 217 $ 179
Building | Minimum      
Property, plant and equipment and depreciation      
Useful life 25 years    
Building | Maximum      
Property, plant and equipment and depreciation      
Useful life 50 years    
Other Capitalized Property Plant and Equipment | Minimum      
Property, plant and equipment and depreciation      
Useful life 2 years    
Other Capitalized Property Plant and Equipment | Maximum      
Property, plant and equipment and depreciation      
Useful life 25 years