Retirement Plans (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended	9 Months Ended
	Jun. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Capitalization of pension and OPEB expense related to engineering and plant construction		$ 18	$ 18
Plan contributions		147
Plan distributions		578
Waiver amount		173
Pension and other postretirement benefits		2,293		$ 1,896
Other comprehensive income (loss) before reclassifications		376
Pension plan liability		$ 146
Increase due to remeasurement	$ 522
Period of plan		5 years
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Settlements, Benefit Obligation		$ 465
Defined Benefit Plan, Settlements Benefit obligation threshold		211
Estimated plan contributions		184
Plan contributions		37
Plan assets		2,299		$ 2,730
Increase (decrease) in pension assets		(431)
Positive investment returns		110
Pension settlement costs		$ 159
Discount rate - used at year end to value obligation		2.70%		3.40%
Pension and other postretirement benefits		$ 1,372		$ 996
Other comprehensive income (loss) before reclassifications		(389)
Pension Benefits [Member] | Northwest Operations [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Positive investment returns		58
Benefit payments		520
Postretirement Costs [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Other comprehensive income (loss) before reclassifications		(16)
PBO		3,671		$ 3,726
Increased in PBO		$ 55