Income Taxes - Schedule of Components of Net Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Deferred tax assets, Depreciation	$ 15	$ 8
Deferred tax assets, Employee benefits	1,382	1,521
Deferred tax assets, Loss provisions	181	172
Deferred tax assets, Tax loss carryforwards	1,540	926
Deferred tax assets, Tax credit carryforwards	652	673
Deferred tax assets, Other	184	311
Deferred tax assets, Gross	3,954	3,611
Deferred tax assets, Valuation allowance	(1,940)	(1,291)	$ (1,151)	$ (1,252)
Deferred tax assets, net	2,014	2,320
Deferred tax liabilities, Depreciation	817	964
Deferred tax liabilities, Employee benefits	8	11
Deferred tax liabilities, Loss provisions	1	2
Deferred tax liabilities, Tax loss carryforwards	0	0
Deferred tax liabilities, Tax credit carryforwards	0	0
Deferred tax liabilities, Other	93	31
Deferred tax liabilities, Gross	919	1,008
Deferred tax liabilities, Valuation allowance	0	0
Deferred tax liabilities, Net	$ 919	$ 1,008