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Benefit Plans - Postemployment Benefit Plans (Details) - Postemployment Benefit Plans - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Defined Benefit Plan Disclosure [Line Items]    
Service cost $ 1 $ 1
Interest cost 1 1
Amortization of net gains (1) (1)
Net periodic benefit costs $ 1 $ 1