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Employee Benefit Plans Plan Assets (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Pension plan assets, fair value $ 93 $ 88 $ 110
Postemployment Benefits [Abstract]      
Postemployment benefit expense 1 3  
Postemployment benefit credit     (1)
Defined Benefit Plan [Abstract]      
Benefit expense related to deferred compensation plans 1 1 $ 1
Equity Funds [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Pension plan assets, fair value 93 [1] 88 [2]  
Fair Value, Inputs, Level 1 [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Pension plan assets, fair value 93 88  
Fair Value, Inputs, Level 1 [Member] | Equity Funds [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Pension plan assets, fair value 93 [1] 88 [2]  
Fair Value, Inputs, Level 2 [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Pension plan assets, fair value 0 0  
Fair Value, Inputs, Level 2 [Member] | Equity Funds [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Pension plan assets, fair value 0 [1] 0 [2]  
Fair Value, Inputs, Level 3 [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Pension plan assets, fair value 0 0  
Fair Value, Inputs, Level 3 [Member] | Equity Funds [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Pension plan assets, fair value 0 [1] $ 0 [2]  
Other Postretirement Benefit Plans, Defined Benefit [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Estimated future contributions in the next fiscal year 10    
Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]      
Postretirement benefit payments - 2018 11    
Postretirement benefit payments - 2019 12    
Postretirement benefit payments - 2020 14    
Postretirement benefit payments - 2021 16    
Postretirement benefit payments - 2022 17    
Postretirement benefit payments - 2023-2027 $ 85    
International Equity [Member] | Equity Funds [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Actual plan asset allocations 8.00% 8.00%  
Fixed Income Funds [Member] | Equity Funds [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Actual plan asset allocations 74.00% 73.00%  
U.S. Equity [Member] | Equity Funds [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Actual plan asset allocations 18.00% 19.00%  
Benefit Obligation [Member]      
Postemployment Benefits [Abstract]      
Postemployment benefit obligations $ 3 $ 6  
Defined Benefit Plan [Abstract]      
Other non-qualified plans benefit obligations deferred compensation $ 10 $ 11  
Minimum [Member] | U.S. Equity [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Postretirement benefit plan asset allocation percentage 0.13    
Minimum [Member] | International Equity [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Postretirement benefit plan asset allocation percentage 0.03    
Minimum [Member] | Fixed Income [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Postretirement benefit plan asset allocation percentage 0.69    
Minimum [Member] | Cash and Cash Equivalents [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Postretirement benefit plan asset allocation percentage 0    
Maximum [Member] | U.S. Equity [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Postretirement benefit plan asset allocation percentage 0.23    
Maximum [Member] | International Equity [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Postretirement benefit plan asset allocation percentage 0.13    
Maximum [Member] | Fixed Income [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Postretirement benefit plan asset allocation percentage 0.79    
Maximum [Member] | Cash and Cash Equivalents [Member]      
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]      
Postretirement benefit plan asset allocation percentage 0.02    
[1] 74% of the amount invested in mutual funds was in fixed income securities; 18% was in U.S. equities and 8% was in international equities.
[2] 73% of the amount invested in mutual funds was in fixed income securities; 19% was in U.S. equities and 8% was in international equities.