Pension and Other Postretirement Benefits (Change In Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Pension benefits [Member]
Change in plan assets:
Fair value of plan assets, beginning of year	$ 3,176	$ 2,932
Actual return on plan assets	429	530
Employer contributions	66	74
Benefits paid	(324)	(360)
Participants’ contributions	0	0
Retiree Medicare drug subsidy	0	0
Fair value of plan assets, end of year	3,347	3,176
Postretirement benefits [Member]
Change in plan assets:
Fair value of plan assets, beginning of year	0	1
Actual return on plan assets	0	(1)
Employer contributions	43	41
Benefits paid	(58)	(59)
Participants’ contributions	12	13
Retiree Medicare drug subsidy	3	5
Fair value of plan assets, end of year	$ 0	$ 0