Income Taxes - Components of Income Tax Provision (Benefit) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
United States - Federal, Current income tax expense (benefit)	$ 1	$ (23)	$ (27)
United States - Federal, Deferred income taxes and other accruals expense (benefit)	(74)	(6)	1,948
United States - State, Current & Deferred income taxes and other accruals expense (benefit)	(45)	0	23
United States, Current & Deferred income taxes and other accruals expense (benefit)	(118)	(29)	1,944
Current (b)	455	179	36
Foreign, Deferred income taxes and other accruals expense (benefit)	(2)	(1,987)	235
Foreign, Current & Deferred income taxes and other accruals expense (benefit)	453	(1,808)	271
Provision (benefit) for income taxes - before adjustments due to income tax law changes	335	(1,837)	2,215
Adjustment of deferred taxes for foreign income tax law changes	0	0	7
Total Provision (Benefit) For Income Taxes	$ 335	$ (1,837)	$ 2,222