Postretirement Benefit Plans (Rollforward of Obligation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligation:
Benefit obligation at beginning of year	$ 914
Benefit obligation at end of year	1,008	$ 914
Other postretirement benefit plans
Change in benefit obligation:
Benefit obligation at beginning of year	52	55
Service cost	0	0	$ 1
Interest cost	2	2	2
Benefits paid	(3)	(3)
Actuarial gain/(loss)	(2)	1
Plan Amendment and other	0	(3)
Benefit obligation at end of year	$ 49	$ 52	$ 55