|**Benefit Plans (Tables)**                            | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
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|**Compensation and Retirement Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Components of net periodic cost (benefit)             | The components of net periodic cost (benefit) are presented in the following table.Periods ended September 30Three MonthsNine Months(In millions)2015201420152014Pension cost (benefit)Service cost$—$3$4$7Interest cost on projected benefit obligation29338599Expected return on plan assets(44)(48)(131)(144)Amortization of net actuarial loss762619Net periodic pension cost (benefit)$(8)$(6)$(16)$(19)Postretirement cost (benefit)Interest cost on projected benefit obligation$—$—$—$1Amortization of prior service credit(1)—(2)(9)Amortization of net actuarial loss——1—Curtailment gain———(86)Net periodic postretirement cost (benefit)$(1)$—$(1)$(94)
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|Periods ended September 30                            | Three Months                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|(In millions)                                         | 2015                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Pension cost (benefit)                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Service cost                                          | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Interest cost on projected benefit obligation         | 29                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Expected return on plan assets                        | (44                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Amortization of net actuarial loss                    | 7                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Net periodic pension cost (benefit)                   | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
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|Postretirement cost (benefit)                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Interest cost on projected benefit obligation         | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Amortization of prior service credit                  | (1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Amortization of net actuarial loss                    | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Curtailment gain                                      | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Net periodic postretirement cost (benefit)            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  

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duration X- DefinitionTabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments.
+ ReferencesReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920
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