Special Charges and Mark-to-Market ("MTM") Adjustments - Components of Special Charges (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating:
Impairment of assets	$ 8	$ 23
Severance and benefit costs	6	14
(Gains) losses on sale of assets and other special charges	4	3
Total operating special charges	18	40	[1]
Nonoperating MTM gains on financial instruments	(17)	(45)
Total special charges and MTM gains on financial instruments	1	(5)
Income tax expense	0	1
Total special charges and MTM gains on financial instruments, net of income tax	$ 1	$ (4)

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2016-02, Leases (Topic 842). See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.