Stockholders' Equity Accumulated Other Comprehensive Income (Loss) (Table) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning		$ (1,394)	$ (1,269)	$ (1,409)	$ (1,288)
Other comprehensive income (loss) before reclassifications		1		(1)
Amortization of prior service cost (credit)	[1]	(3)	(2)	(5)	(2)
Amortization of net actuarial loss (gain)	[1]	26	26	51	51
Tax benefit (expense) for items of other comprehensive income		(6)	(6)	(12)	(12)
Other comprehensive income (loss), net of tax		18	18	33	37
Balance, ending		(1,376)	(1,251)	(1,376)	(1,251)
Income tax expense (benefit)		12	36	56	67
Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning		(1,390)	(1,264)	(1,407)	(1,283)
Amortization of prior service cost (credit)	[1]	(3)	(2)	(5)	(2)
Amortization of net actuarial loss (gain)	[1]	26	26	51	51
Tax benefit (expense) for items of other comprehensive income		(6)	(6)	(12)	(12)
Other comprehensive income (loss), net of tax		17	18	34	37
Balance, ending		(1,373)	(1,246)	(1,373)	(1,246)
Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning		(4)	(5)	(2)	(5)
Other comprehensive income (loss) before reclassifications		1		(1)
Other comprehensive income (loss), net of tax		1		(1)
Balance, ending		(3)	(5)	(3)	(5)
Reclassification out of AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax expense (benefit)		$ 6	$ 6	$ 12	$ 12

[1] These accumulated comprehensive loss components are included in the computation of net periodic benefit cost. See Note 17: Employee Pension and Other Postretirement Benefits. The tax benefit associated with amounts reclassified from accumulated other comprehensive loss for each of the three months ended June 30, 2020 and 2019, was $6 million. The tax benefit associated with amounts reclassified from accumulated other comprehensive loss for each of the six months ended June 30, 2020 and 2019, was $12 million.