Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax And Carryforwards [Line Items]
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability	$ (82)	$ (1,200)
Deferred Other Tax Expense (Benefit)	(710)	(797)
Excess over tax basis	38
Interest and penalties accrued for unrecognized tax benefits, current period	2	2	$ 3
Interest and penalties accrued for unrecognized tax benefits, total	8	5	3
Unrecognized tax benefits that would impact the effective tax rate	145	78	$ 17
General Business Tax Credit Carryforward [Member]
Income Tax And Carryforwards [Line Items]
Operating loss carryforward, amount to expire	72
Federal [Member]
Income Tax And Carryforwards [Line Items]
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability	(569)	(442)
Operating loss carryforward	2,600	2,900
State [Member]
Income Tax And Carryforwards [Line Items]
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability	(42)
Operating loss carryforward	9,000	8,900
Foreign Tax Authority [Member]
Income Tax And Carryforwards [Line Items]
Operating loss carryforward	$ 91	$ 95