Stockholders' Equity Accumulated Other Comprehensive Income (Loss) (Table) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning		$ (935)	$ (833)	$ (951)	$ (845)
Other comprehensive income (loss) before reclassifications		3		7
Amortization of prior service cost (credit)	[1]			(1)
Amortization of net actuarial loss (gain)	[1]	23	19	46	39
Tax benefit (expense) for items of other comprehensive income		(10)	(7)	(20)	(15)
Other comprehensive income (loss), net of tax		16	12	32	24
Balance, ending		(919)	(821)	(919)	(821)
Income tax expense (benefit)		71	66	99	107
Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning		(935)	(831)	(948)	(843)
Amortization of prior service cost (credit)	[1]			(1)
Amortization of net actuarial loss (gain)	[1]	23	19	46	39
Tax benefit (expense) for items of other comprehensive income		(9)	(7)	(18)	(15)
Other comprehensive income (loss), net of tax		14	12	27	24
Balance, ending		(921)	(819)	(921)	(819)
Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning			(2)	(3)	(2)
Other comprehensive income (loss) before reclassifications		3		7
Tax benefit (expense) for items of other comprehensive income		(1)		(2)
Other comprehensive income (loss), net of tax		2		5
Balance, ending		2	(2)	2	(2)
Reclassification out of AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax expense (benefit)		$ 9	$ 7	$ 18	$ 15

[1] These accumulated comprehensive income (loss) components are included in the computation of net periodic benefit cost. See Note 16: Employee Pension and Other Postretirement Benefits. The tax benefit associated with amounts reclassified from accumulated other comprehensive income (loss) for the three months ended June 30, 2017 and 2016, was $9 million and $7 million, respectively. The tax benefit associated with amounts reclassified from accumulated other comprehensive income (loss) for the six months ended June 30, 2017 and 2016, was $18 million and $15 million, respectively.