Income Taxes - Schedule of Expiration Periods of Deferred Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Tax Credit Carryforward [Line Items]
Tax loss carryforwards	$ 3,305
Tax credit carryforwards	638
Other	1,144
Valuation allowance	(2,584)	$ (1,940)	$ (1,291)	$ (1,151)
Deferred tax assets, net	2,503	$ 2,014
Expires within 10 years
Tax Credit Carryforward [Line Items]
Tax loss carryforwards	81
Tax credit carryforwards	531
Other	0
Valuation allowance	(467)
Deferred tax assets, net	145
Expires within 11-20 years
Tax Credit Carryforward [Line Items]
Tax loss carryforwards	781
Tax credit carryforwards	97
Other	0
Valuation allowance	(646)
Deferred tax assets, net	232
No expiration
Tax Credit Carryforward [Line Items]
Tax loss carryforwards	2,443
Tax credit carryforwards	10
Other	84
Valuation allowance	(1,376)
Deferred tax assets, net	1,161
Other
Tax Credit Carryforward [Line Items]
Tax loss carryforwards	0
Tax credit carryforwards	0
Other	1,060
Valuation allowance	(95)
Deferred tax assets, net	$ 965