Postretirement Benefit Plans (Amounts Recognized in OCI) (Details) - Other Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure
Service cost	$ 0
Interest cost	2	$ 2	$ 2
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	3	4	4
Amortization of net actuarial loss	2	2	2
Net periodic benefit cost	$ 1	$ 0	$ 0