Retirement Plans (Projected Benefit Obligation, Fair Values Of Plan Assets And Amounts Recognized In The Balance Sheet) (Details) - USD ($) $ in Millions		12 Months Ended
Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in projected benefit obligation (PBO) [Roll Forward]
Benefits paid		$ (538)
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		2,730
Employer contribution	$ 27
Fair value of plan assets at end of year	2,507	2,507	$ 2,730
Amounts recognized in the consolidated balance sheet [Abstract]
Pension and other postretirement benefits - current	(48)	(48)	(43)
Pension and other postretirement benefits - noncurrent	(2,195)	(2,195)	(1,896)
Elimination of future compensation increases		20
Pension Benefits [Member]
Change in projected benefit obligation (PBO) [Roll Forward]
PBO at beginning of year		3,726	3,173
Service cost		95	82	$ 90
Interest cost		108	130	125
Actuarial (gain) loss		506	603
Benefits paid		(73)	(65)
Impact of Divestiture of Northwest Operations		(189)
Settlements		(465)	(235)
Special termination benefits			38
PBO at end of year	3,708	3,708	3,726	3,173
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		2,730	2,348
Fair value of plan assets for the Northwest Operations		(70)
Actual return on plan assets		321	516
Employer contribution		64	166
Settlements		(465)	(235)
Benefits paid		(73)	(65)
Fair value of plan assets at end of year	2,507	2,507	2,730	2,348
Funded status	(1,201)	(1,201)	(996)
Amounts recognized in the consolidated balance sheet [Abstract]
Pension and other postretirement benefits - noncurrent	(1,201)	(1,201)	(996)
Accumulated other comprehensive (gain) loss	915	915	899	754
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Change in projected benefit obligation (PBO) [Roll Forward]
PBO at beginning of year		972	965
Service cost		20	20	21
Interest cost		33	41	38
Plan amendments			(149)
Plan participants' contributions		9	7
Actuarial (gain) loss		100	129
Benefits paid		(61)	(47)
Impact of Divestiture of Northwest Operations		(31)
Special termination benefits			6
PBO at end of year	1,042	1,042	972	965
Change in plan assets [Roll Forward]
Plan participants' contributions		9	7
Employer contribution		52	40
Benefits paid		(61)	(47)
Funded status	(1,042)	(1,042)	(972)
Amounts recognized in the consolidated balance sheet [Abstract]
Pension and other postretirement benefits - current	(48)	(48)	(43)
Pension and other postretirement benefits - noncurrent	(994)	(994)	(900)
Pension and other postretirement benefits - AHFS			(29)
Accumulated other comprehensive (gain) loss	$ 74	$ 74	$ (45)	$ (41)

Defined Benefit Plan, Decrease In Obligation Due To Curtailment

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