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Pension Benefits Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Retirement Benefits [Abstract]      
Defined Benefit Pension Plan, Postemployment Benefit Period 5 years    
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year $ 48    
Defined Contribution Plan, Cost $ 37 $ 36 $ 36