Asset Retirement Obligations - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Asset Retirement Obligation [Line Items]
Fair value of sinking fund deposits legally restricted for purposes of settling asset retirement obligations	$ 102	$ 79
Drilling License | South Arne Field, offshore Denmark
Asset Retirement Obligation [Line Items]
License agreement extension period	20 years
License agreement expiration year	2047