|**Benefit Plans (Tables)**                            | 3 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.Three months ended March 31(In millions)20152014Pension cost (benefit)Service cost$2$3Interest cost on projected benefit obligation2833Expected return on plan assets(43)(48)Amortization of net actuarial loss96Net periodic pension cost (benefit)$(4)$(6)Postretirement cost (benefit)Amortization of prior service credit$—$(4)Net periodic postretirement cost (benefit)$—$(4)
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|Three months ended March 31                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|(In millions)                                         | 2015                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Pension cost (benefit)                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Service cost                                          | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Interest cost on projected benefit obligation         | 28                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Expected return on plan assets                        | (43                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Amortization of net actuarial loss                    | 9                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Net periodic pension cost (benefit)                   | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
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|Postretirement cost (benefit)                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Amortization of prior service credit                  | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|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+ Details**Name:**
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