Acquisitions, Divestitures, and Assets Held for Sale - Acquisitions (Detail) (USD $)	12 Months Ended				0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012	Nov. 25, 2014
Business Acquisition [Line Items]
Purchase price	$ 1,527,000,000	$ 473,000,000		$ 0
Goodwill	5,576,000,000	5,492,000,000		5,492,000,000
Revenues	18,470,000,000	14,581,000,000		13,411,000,000
Gathering and Processing Assets in the Delaware basin [Member]
Business Acquisition [Line Items]
Purchase price					1,554,000,000
Current assets					46,000,000
Properties and equipment					441,000,000
Other intangible assets					836,000,000
Accounts payable					(13,000,000)
Accrued expenses					(25,000,000)
Deferred income taxes					(1,000,000)
Asset retirement obligations					(9,000,000)
Goodwill					279,000,000
Total assets acquired and liabilities assumed					1,554,000,000
Goodwill amortizable for tax purposes					279,000,000
Revenues
Revenue and earnings that would have been recognized had the acquisition occurred on January 1
Moxa Oil and Gas Properties [Member]
Business Acquisition [Line Items]
Purchase price		310,000,000	[1]
Properties and equipment		306,000,000
Ownership interest purchased		100.00%
Marcellus Interest in Gas-Gathering Systems [Member]
Business Acquisition [Line Items]
Purchase price		135,000,000
Ownership interest purchased		33.75%
Mont Belvieu Joint Venture [Member]
Business Acquisition [Line Items]
Purchase price		78,000,000
Ownership interest purchased		25.00%
Intrastate Pipeline in Wyoming [Member]
Business Acquisition [Line Items]
Purchase price		$ 28,000,000
Ownership interest purchased		100.00%

[1] Includes $306 million that represents the fair value of the oil and gas properties acquired.