Reclassifications from Accumulated Other Comprehensive Income (Loss) (Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
General and administrative expenses	$ 233		$ 247	$ 246
Provision (benefit) for income taxes	(93)		(29)	(2,005)
Net Income (Loss)	1,046	[1]	$ (2,643)	$ (4,556)
Reclassified from Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income (Loss)	2
Pension And Other Postretirement [Member] | Reclassified from Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
General and administrative expenses	2
Provision (benefit) for income taxes
Net Income (Loss)	$ 2

[1] In 2017, deferred tax activity incurred in other comprehensive income was offset by a valuation allowance.