Postretirement Benefit Plans (Rollforward of Obligation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation:
Benefit obligation at beginning of year	$ 1,008
Benefit obligation at end of year	1,199	$ 1,008
Other postretirement benefit plans
Change in benefit obligation:
Benefit obligation at beginning of year	49	52
Service cost	0
Interest cost	2	2	$ 2
Benefits paid	(3)	(3)
Actuarial gain/(loss)	1	(2)
Plan Amendment and other	(5)	0
Benefit obligation at end of year	$ 44	$ 49	$ 52