|**Leases (Tables)**                   | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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|**Leases, Operating [Abstract]**      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Assets and liabilities                | The following table presents operating lease ROU assets and lease liabilities.(In millions)December 31, 2019Operating lease ROU assets$220Operating lease liabilities301                                                                                                                                                                                                                                                                                                                            
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|                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|(In millions)                         | December 31, 2019                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Operating lease ROU assets            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Operating lease liabilities           | 301                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Operating lease, liability, maturity  | The following table presents the maturities of operating lease liabilities as ofDecember 31, 2019.(In millions)Operating Leases2020$38202143202240202334202429Thereafter184Total lease payments368Less: Discount(67)Total operating lease liabilities$301The table below presents the expected future minimum lease payments to be made under non-cancelable operating leases as ofDecember 31, 2018.(In millions)Future Minimum Lease Payments2019$35202039202141202238202332Thereafter200Total$385
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|                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|(In millions)                         | Operating Leases                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|2020                                  | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|2021                                  | 43                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|2022                                  | 40                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|2023                                  | 34                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|2024                                  | 29                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Thereafter                            | 184                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Total lease payments                  | 368                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Less: Discount                        | (67                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Total operating lease liabilities     | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
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|                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|(In millions)                         | Future Minimum Lease Payments                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|2019                                  | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|2020                                  | 39                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|2021                                  | 41                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|2022                                  | 38                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|2023                                  | 32                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Thereafter                            | 200                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Total                                 | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Lease cost                            | The following table presents the weighted average remaining lease term for operating leases and weighted average discount rate used in calculating operating lease right-of-use assets.December 31, 2019Weighted average remaining lease term10.8 yearsWeighted average discount rate3.4%                                                                                                                                                                                                           
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|                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                      | December 31, 2019                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Weighted average remaining lease term | 10.8 years                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Weighted average discount rate        | 3.4                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 

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