Postretirement Benefit Plans (Amounts Recognized in OCI) (Details) - Other Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure
Service cost	$ 0	$ 0	$ 1
Interest cost	2	2	2
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	4	4	3
Amortization of net actuarial loss	2	2	2
Net periodic benefit cost	$ 0	$ 0	$ 2