Impairment - Additional Information (Detail) - USD ($)		12 Months Ended
	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Impairments [Line Items]
Impairment charge, pre-tax		$ 67,000,000	$ 1,616,000,000	$ 0
Impairment charge, after-tax and noncontrolling interest		21,000,000
Goodwill impairment charge, pre-tax		$ 0	1,483,000,000
Goodwill impairment charge, after-tax			1,483,000,000
Legacy conventional North Dakota Assets
Impairments [Line Items]
Impairment charge, pre-tax			133,000,000
Impairment charge, after-tax			83,000,000
Onshore Reporting Unit - Post Segment Change
Impairments [Line Items]
Goodwill impairment charge, pre-tax			385,000,000
Offshore Reporting Unit - Post Segment Change
Impairments [Line Items]
Goodwill impairment charge, pre-tax			1,098,000,000
Bakken Midstream
Impairments [Line Items]
Goodwill impairment charge, pre-tax			$ 0
Offshore and Onshore Reporting Units - Pre-segment Change
Impairments [Line Items]
Goodwill impairment charge, pre-tax	$ 0