Reclassifications from Accumulated Other Comprehensive Income (Loss) (Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (loss), net	$ 3		$ 6	$ 2		$ 8
Provision (Benefit) for Income Taxes
Net Income	$ 51	[1]	$ 284	259	[1]	$ 635
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.