Reclassifications from Accumulated Other Comprehensive Income (Loss) (Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018		Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (loss), net	$ (1)		$ 1
Provision (benefit) for income taxes
Net Income	208	[1]	$ 351
Reclassified from Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income
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
Provision (benefit) for income taxes
Net Income

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