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Retirement Benefits Plans Retirement Benefits Plans - Fair Value of Other Postretirement Benefits Plan Assets (Details 12) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Fair Value of Other Postretirement Benefits Plan Assets [Line Items]    
Global equities $ 44 $ 54
Fixed income securities 18 24
United States treasuries 20 37
Cash equivalents 11 1
Total other postretirement benefits plan assets $ 93 116
VEBA target trust allocation in diversified global equities 50.00%  
VEBA target trust allocation in fixed income securities 50.00%  
Quoted prices in active markets for identical assets (Level 1) [Member]    
Fair Value of Other Postretirement Benefits Plan Assets [Line Items]    
Global equities $ 0 0
Fixed income securities 0 0
United States treasuries 20 37
Cash equivalents 11 1
Total other postretirement benefits plan assets 31 38
Other observable inputs (Level 2) [Member]    
Fair Value of Other Postretirement Benefits Plan Assets [Line Items]    
Global equities 44 54
Fixed income securities 18 24
United States treasuries 0 0
Cash equivalents 0 0
Total other postretirement benefits plan assets 62 78
Unobservable inputs (Level 3) [Member]    
Fair Value of Other Postretirement Benefits Plan Assets [Line Items]    
Global equities 0 0
Fixed income securities 0 0
United States treasuries 0 0
Cash equivalents 0 0
Total other postretirement benefits plan assets $ 0 $ 0