Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other net periodic benefit costs	$ 14	$ 19	$ 102
Net interest and other	(226)	(270)	(332)
Income (loss) from continuing operations before income taxes	1,427	(454)	(1,164)
(Provision) benefit for income taxes	(331)	(376)	(923)
Income (loss) from continuing operations	1,096	(830)	(2,087)
Income (loss) from discontinued operations	0	(4,893)	(53)
Net income (loss)	1,096	(5,723)	$ (2,140)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income (loss) from continuing operations before income taxes	(15)	23
(Provision) benefit for income taxes	1	(40)
Income (loss) from continuing operations	(14)	(17)
Net income (loss)	(14)	(47)
Amortization of prior service credit | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other net periodic benefit costs	(18)	(17)
Amortization of actuarial loss | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other net periodic benefit costs	12	9
Net settlement loss | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other net periodic benefit costs	21	32
Recognized gain on terminated derivative hedge | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net interest and other	0	46
Ineffective portion of derivative hedge | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net interest and other	0	1
Foreign currency hedges | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income (loss) from discontinued operations	$ 0	$ (30)