Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Examination [Line Items]
Gross deferred tax asset related to net operating loss carryforwards		$ 4,029,000,000	$ 5,767,000,000
Gross deferred tax asset related to foreign net operating loss carryforwards		1,386,000,000
Gross deferred tax asset related to net U.S. federal operating loss carryforwards		$ 2,180,000,000
Year in which majority portion of U.S. federal net operating loss carryforwards begin to expire		2034
Gross deferred tax asset related to net operating loss carryforwards for various U.S. states		$ 463,000,000
Deferred tax asset related to foreign net operating loss carryforwards, net of valuation allowance		9,000,000
Alternative minimum tax credit carryforwards		53,000,000
Other business credit carryforwards		15,000,000
Deferred tax asset related to business credit carryforwards, net of valuation allowance		4,000,000
Foreign tax credit carryforwards - Before valuation allowance		$ 70,000,000
Year in which foreign tax credit carryforwards begin to expire		2018
Valuation allowance against net deferred tax assets		$ 5,199,000,000	$ 5,450,000,000
Period of cumulative loss incurred		3 years
Tax accrued on deemed repatriation of unremitted earnings of foreign subsidiaries		$ 0
Federal corporate tax rate		35.00%	35.00%	35.00%
Refundable alternative minimum tax credit if not offset by regular tax liability		$ 4,000,000
Increase to net deferred tax asset and benefit to deferred tax expense due to change in tax law		4,000,000
Unrecognized tax benefits that would impact effective income tax rate		30,000,000	$ 233,000,000
Accrued interest and penalties		23,000,000	$ 29,000,000
Minimum
Income Tax Examination [Line Items]
Unrecognized tax benefits decrease reasonably possible		58,000,000
Maximum
Income Tax Examination [Line Items]
Unrecognized tax benefits decrease reasonably possible		139,000,000
Tax Reform - Tax Rate
Income Tax Examination [Line Items]
Decrease in net deferred tax asset due to tax rate change		(1,476,000,000)
Tax Reform - Territorial Regime
Income Tax Examination [Line Items]
Decrease in net deferred tax asset due to tax rate change		$ 110,000,000
Scenario Forecast
Income Tax Examination [Line Items]
Federal corporate tax rate	21.00%
Foreign
Income Tax Examination [Line Items]
Operating loss carryforwards expiration date		Jan. 01, 2024
U.S. Federal
Income Tax Examination [Line Items]
Operating loss carryforwards expiration date		Jan. 01, 2028
U.S. State
Income Tax Examination [Line Items]
Operating loss carryforwards expiration date		Jan. 01, 2018