Retirement Plans (Narrative) (Details)		12 Months Ended
	Jun. 30, 2019 USD ($)	Dec. 31, 2020	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) item
Retirement Plans [Line Items]
Pension & OPEB Descriptions			Pension Plans – We provide defined benefit retirement income to eligible non-union employees through qualified and non-qualified (supplemental) pension plans. Qualified and non-qualified pension benefits are based on years of service and the highest compensation during the latest years of employment, with specific reductions made for early retirements. Non-union employees hired on or after January 1, 2018 are no longer eligible for pension benefits, but are eligible for an enhanced 401(k) benefit as described below in other retirement programs. Other Postretirement Benefits (OPEB) – We provide medical and life insurance benefits for eligible retirees hired before January 1, 2004. These benefits are funded as medical claims and life insurance premiums are paid.
Changes in fair value period			5 years
OPEB Plan amendment (Note 6)	$ (92,000,000)		$ (92,000,000)
Defined benefit plans	69,000,000		(42,000,000)	$ (62,000,000)	$ (103,000,000)
Deferred Tax Assets, Gross	$ 23,000,000		533,000,000	501,000,000
Future net periodic OPEB cost amortization duration	8 years
Curtailment cost					20,000,000
Special termination cost					$ 49,000,000
Significant transfers in or out of Levels 1, 2, or 3			0	0
Pension Plan Master Trust future commitments for additonal contributions private equtiy partnerships			189,000,000	248,000,000
Pension Plan Master Trust future commitments for additional contributions real estate partnerships and funds			8,000,000	54,000,000
Management Positions. [Member]
Retirement Plans [Line Items]
Number of positions eliminated | item					460
Pension [Member]
Retirement Plans [Line Items]
Accumulated benefit obligation			498,000,000	446,000,000
Accumulated benefit obligation.			$ 4,500,000,000	$ 3,900,000,000
Curtailment cost					$ 20,000,000
Special termination cost					$ 49,000,000
Discount rate - benefit obligations			3.26%	4.23%
Actual return (loss) on pension plan assets, net of fees			20.00%	(2.00%)	19.00%
OPEB [Member]
Retirement Plans [Line Items]
OPEB Plan amendment (Note 6)			$ (92,000,000)
Discount rate - benefit obligations			3.13%	4.17%
Health care cost trend rate (employees under 65)			5.87%	6.09%	6.31%
Ultimate health care cost trend rate			4.50%	4.50%	4.50%
Year ultimate trend rate reached			2038	2038	2038
OPEB [Member] | Total 2015 Forecast [Member]
Retirement Plans [Line Items]
Health care cost trend rate (employees under 65)		5.64%
Ultimate health care cost trend rate		4.50%
Year ultimate trend rate reached		2038