Income Taxes - Reconciliation of Tax of Income Before Income Taxes and Total Tax Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Income Tax [Line Items]
Income tax expense (benefit) at U.S. statutory rate	$ (9,879)	$ (983)	$ 1,368
State income tax, less federal benefit	(32)	(27)	29
Taxes related to foreign operations	(696)	(154)	236
Tax credits	(6)		6
Tax on distributed foreign earnings	726	311	225
Foreign tax credit carryforwards	(2,090)
Deferred tax on undistributed foreign earnings	1,903	1,654
Goodwill impairment		483
Net change in tax contingencies	20	(3)	(10)
Valuation allowances	5,253	478	132
All other, net	(49)	(2)	(58)
Provision (benefit) for income taxes	(5,469)	663	$ 1,928
United States [Member]
Schedule Of Income Tax [Line Items]
Deferred tax on undistributed foreign earnings		$ 560
United Kingdom [Member]
Schedule Of Income Tax [Line Items]
Change in U.K. tax rate	$ (619)