Retirement Plans (Reconciliation of Benefit Obligations And Plan or Trust Assets And Resulting Funded Status Of Defined Benefit Retirement Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Change in Benefit Obligation
Benefit obligation at beginning of year	$ (15,720)	$ (14,212)
Service cost	(111)	(180)	$ (168)
Interest cost	(600)	(532)	(453)
Acquisitions	0	(2,758)
Amendments	(3)	15
Actuarial gain (loss)	(2,446)	1,183
Settlement/curtailment/other	(33)	23
Benefits paid	806	741
Benefit obligation at end of year	(18,107)	(15,720)	(14,212)
Change in Plan/Trust Assets
Fair value of assets at beginning of year	11,532	10,130
Actual return on plan assets	2,206	(749)
Acquisitions	0	2,328
Employer contributions	185	571
Settlement/curtailment/other	39	(26)
Benefits paid	(785)	(722)
Fair value of assets at end of year	13,177	11,532	10,130
Funded status at end of year	(4,930)	(4,188)
Other Post-retirement Benefits
Change in Benefit Obligation
Benefit obligation at beginning of year	(935)	(996)
Service cost	(8)	(10)	(9)
Interest cost	(35)	(33)	(30)
Acquisitions	0	(62)
Amendments	(8)	0
Actuarial gain (loss)	(101)	78
Settlement/curtailment/other	(4)	21
Benefits paid	64	67
Benefit obligation at end of year	(1,027)	(935)	(996)
Change in Plan/Trust Assets
Fair value of assets at beginning of year	570	541
Actual return on plan assets	117	(4)
Acquisitions	0	77
Employer contributions	2	1
Settlement/curtailment/other	0	0
Benefits paid	(45)	(45)
Fair value of assets at end of year	644	570	$ 541
Funded status at end of year	$ (383)	$ (365)