Income Taxes - Components of Income Tax Provision (Benefit) for Continuing Operations (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
United States - Federal, Current income tax expense (benefit)	$ (23)	$ (27)	$ (7)
United States - Federal, Deferred income taxes and other accruals expense (benefit)	(6)	1,948	(995)
United States - State, Current & Deferred income taxes and other accruals expense (benefit)	0	23	(61)
United States, Current & Deferred income taxes and other accruals expense (benefit)	(29)	1,944	(1,063)
Foreign, Current income tax expense (benefit)	179	36	4
Foreign, Deferred income taxes and other accruals expense (benefit)	(1,987)	235	(231)
Foreign, Current & Deferred income taxes and other accruals expense (benefit)	(1,808)	271	(227)
Provision (benefit) for income taxes - before adjustments due to income tax law changes	(1,837)	2,215	(1,290)
Adjustment of deferred taxes for foreign income tax law changes	0	7	(9)
Total Provision (Benefit) For Income Taxes	$ (1,837)	$ 2,222	$ (1,299)