Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax [Line Items]
Current income tax liability		$ 560
Deferred income tax liability on undistributed foreign earnings			$ 560
Deferred income tax expense on foreign undistributed earnings			311
Deferred tax benefit	$ 576	271	1,083
Increase in valuation allowances	33	3,900	966
Foreign tax credit carryforward, amount	2,226	2,090
Tax expense (benefit) recorded for interest and penalties	0	1	1
Accrued for payment of interest and penalties	0	1	$ 0
Reserve for uncertain tax positions related to the current year	4	$ (19)
Settlements	3
United States [Member]
Income Tax [Line Items]
Operating loss carryforwards	2,452
Operating loss carryforwards subject to annual limitation	197
Canada [Member]
Income Tax [Line Items]
Operating loss carryforwards	125
Capital loss carryforwards	$ 829
Her Majesty's Revenue and Customs (HMRC) [Member]
Income Tax [Line Items]
Supplementary charge, percent	10.00%	20.00%	32.00%
Deferred tax benefit	$ 238	$ 414