Acquisitions and Divestitures - Additional Information - 2016 Activity (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014
Business Acquisition [Line Items]
Proceeds from sale of certain non-core assets		$ 440
Refundable deposits		$ 174	$ 174	$ 0
Leasehold and property acquisition			181	367	[1]	$ 1,475	[1]
Proceeds from divestiture of other oil and gas properties			134	268		96
Gain (loss) on divestiture of other oil and gas properties			$ 21	$ 135		$ (216)
Scottish Area Gas Evacuation System [Member]
Business Acquisition [Line Items]
Percentage of ownership		30.28%	30.28%
Beryl Pipeline [Member]
Business Acquisition [Line Items]
Percentage of ownership		60.56%	60.56%
Scenario, Forecast [Member]
Business Acquisition [Line Items]
Gain from sale of certain non-core assets	$ 300

[1] Financial information for 2015 and 2014 has been recast to reflect retrospective application of the successful efforts method of accounting. See Note 1.