|**Leases (Tables)**                                             | 9 Months Ended                                                                                                                                                                                                                                                                                                
|--------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**Leases [Abstract]**                                           |                                                                                                                                                                                                                                                                                                               
|Assets and liabilities, lessee                                  | The following table presents operating lease ROU assets and lease liabilities.(In millions)September 30, 2019Operating lease ROU assets$223Operating lease liabilities304                                                                                                                                     
|                                                               
|                                                                |                                                                                                                                                                                                                                                                                                               
|(In millions)                                                   | September 30, 2019                                                                                                                                                                                                                                                                                            
|Operating lease ROU assets                                      | $                                                                                                                                                                                                                                                                                                             
|Operating lease liabilities                                     | 304                                                                                                                                                                                                                                                                                                           
|Maturities of operating lease liabilities                       | The following table presents the maturities of operating lease liabilities as ofSeptember 30, 2019.(In millions)Operating Leases2019 (Excluding the nine months ended September 30, 2019)$6202039202142202239202334Thereafter213Total lease payments373Less: Discount(69)Total operating lease liabilities$304
|                                                               
|                                                                |                                                                                                                                                                                                                                                                                                               
|(In millions)                                                   | Operating Leases                                                                                                                                                                                                                                                                                              
|2019 (Excluding the nine months ended September 30, 2019)       | $                                                                                                                                                                                                                                                                                                             
|2020                                                            | 39                                                                                                                                                                                                                                                                                                            
|2021                                                            | 42                                                                                                                                                                                                                                                                                                            
|2022                                                            | 39                                                                                                                                                                                                                                                                                                            
|2023                                                            | 34                                                                                                                                                                                                                                                                                                            
|Thereafter                                                      | 213                                                                                                                                                                                                                                                                                                           
|Total lease payments                                            | 373                                                                                                                                                                                                                                                                                                           
|Less: Discount                                                  | (69                                                                                                                                                                                                                                                                                                           
|Total operating lease liabilities                               | $                                                                                                                                                                                                                                                                                                             
|Lease terms and discount rates                                  | 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.September 30, 2019Weighted average remaining lease term10.9 yearsWeighted average discount rate3.4%                    
|                                                               
|                                                                |                                                                                                                                                                                                                                                                                                               
|                                                                | September 30, 2019                                                                                                                                                                                                                                                                                            
|Weighted average remaining lease term                           | 10.9 years                                                                                                                                                                                                                                                                                                    
|Weighted average discount rate                                  | 3.4                                                                                                                                                                                                                                                                                                           
|Schedule of future minimum rental payments for operating leases | The following table 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                                                               
|                                                               
|                                                                |                                                                                                                                                                                                                                                                                                               
|(In millions)                                                   | Future Minimum Lease Payments                                                                                                                                                                                                                                                                                 
|2019                                                            | $                                                                                                                                                                                                                                                                                                             
|2020                                                            | 39                                                                                                                                                                                                                                                                                                            
|2021                                                            | 41                                                                                                                                                                                                                                                                                                            
|2022                                                            | 38                                                                                                                                                                                                                                                                                                            
|2023                                                            | 32                                                                                                                                                                                                                                                                                                            
|Thereafter                                                      | 200                                                                                                                                                                                                                                                                                                           
|Total                                                           | $                                                                                                                                                                                                                                                                                                             

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