Reclassifications from Accumulated Other Comprehensive Income (Loss) (Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended							9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018		Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Income, Net	$ (2)			$ (1)				$ (7)	$ 1
Provision for income taxes	10			0				(401)	0
Net income	$ 49	$ 138	$ 594	$ (29)	[1]	$ 51	$ 208	781	$ 230	[1]
Amount Reclassified from Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income								5
Amortization of prior service cost and net loss | Amount Reclassified from Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Income, Net								7
Provision for income taxes								2
Net income								$ 5

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