Reclassifications from Accumulated Other Comprehensive Income (Loss) (Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (loss), net														$ 5		$ (4)
Provision (benefit) for income taxes													$ 1	(93)		(29)
Net Income (Loss)	$ 307	$ (29)	$ 51	$ 208	$ 334	$ 77	$ 284	$ 351	$ (210)	$ (708)	$ (593)	$ (1,132)	537	$ 1,046	[1]	$ (2,643)
Reclassified from Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income (Loss)													10
Pension And Other Postretirement [Member] | Reclassified from Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (loss), net													10
Provision (benefit) for income taxes
Net Income (Loss)													$ 10

[1] In 2018 and 2017, deferred tax activity incurred in other comprehensive income was offset by a valuation allowance.