Comprehensive Loss (Accumulated Other Comprehensive Loss, Net Of Tax) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning	$ 1,600	$ 2,274	$ 4,519
Net current-period other comprehensive income (loss)	(108)	(97)	21
Balance, ending	(4,394)	1,600	2,274
Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Impact of adoption of new accounting principle	(79)
Deferred Taxes On Pension And OPEB Costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Deferred tax items	204	250	223	$ 231
Defined Benefit Plans [Member] | Pension Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning	(489)	(345)	(403)
Other comprehensive income (loss) before reclassifications	(201)	(191)	(12)
Amounts reclassified from accumulated other comprehensive income (loss)	89	47	70
Net current-period other comprehensive income (loss)	(112)	(144)	58
Balance, ending	(684)	(489)	(345)
Defined Benefit Plans [Member] | Pension Benefits [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Impact of adoption of new accounting principle	(83)
Defined Benefit Plans [Member] | Postretirement Costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning	26	(21)	16
Other comprehensive income (loss) before reclassifications	17	51	(31)
Amounts reclassified from accumulated other comprehensive income (loss)	(13)	(4)	(6)
Net current-period other comprehensive income (loss)	4	47	(37)
Balance, ending	34	26	(21)
Defined Benefit Plans [Member] | Postretirement Costs [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Impact of adoption of new accounting principle	4
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning	(463)	(366)	(387)
Other comprehensive income (loss) before reclassifications	(184)	(140)	(43)
Amounts reclassified from accumulated other comprehensive income (loss)	76	43	64
Net current-period other comprehensive income (loss)	(108)	(97)	21
Balance, ending	(650)	$ (463)	$ (366)
Accumulated Other Comprehensive Loss [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Impact of adoption of new accounting principle	$ (79)