|**Benefit Plans**                                     | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                  
|----------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**Compensation and Retirement Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Benefit Plans                                         | NoteG. Benefit PlansThe components of net periodic cost (benefit) are presented in the following table.Periods ended September 30Three MonthsNine Months(In millions)2016201520162015Pension cost (benefit)Service cost$—$—$—$4Interest cost on projected benefit obligation29298585Expected return on plan assets(41)(44)(121)(131)Amortization of net actuarial loss972826Net periodic pension cost (benefit)$(3)$(8)$(8)$(16)
|                                                     
|                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Periods ended September 30                            | Three Months                                                                                                                                                                                                                                                                                                                                                                                                                    
|(In millions)                                         | 2016                                                                                                                                                                                                                                                                                                                                                                                                                            
|Pension cost (benefit)                                |                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Service cost                                          | $                                                                                                                                                                                                                                                                                                                                                                                                                               
|Interest cost on projected benefit obligation         | 29                                                                                                                                                                                                                                                                                                                                                                                                                              
|Expected return on plan assets                        | (41                                                                                                                                                                                                                                                                                                                                                                                                                             
|Amortization of net actuarial loss                    | 9                                                                                                                                                                                                                                                                                                                                                                                                                               
|Net periodic pension cost (benefit)                   | $                                                                                                                                                                                                                                                                                                                                                                                                                               

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