Acquisitions and Divestitures - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended			3 Months Ended		0 Months Ended
	Oct. 31, 2014	Dec. 31, 2014 Property Hotel	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2015	Mar. 31, 2014	Sep. 30, 2014	Oct. 15, 2012	Oct. 01, 2012	Jul. 02, 2012
Business Acquisition and Divestitures [Line Items]
Number of remaining natural gas and oil properties		0
Purchase price	$ 230	$ 448	$ 235	$ 987
Goodwill recorded		374	357	412
Number of hotel properties acquired		3
Scenario, Forecast [Member]
Business Acquisition and Divestitures [Line Items]
Purchase price					170
CNA Acquired Hardy [Member]
Business Acquisition and Divestitures [Line Items]
Purchase price received										231
Evangeline Pipeline System [Member]
Business Acquisition and Divestitures [Line Items]
Purchase price	295
Bluegrass Project [Member]
Business Acquisition and Divestitures [Line Items]
Previous period capitalized costs recorded as charge in present period in other operating expenses, net of tax and noncontrolling interest						55
Bluegrass Project [Member] | Other Operating Expenses [Member]
Business Acquisition and Divestitures [Line Items]
Previous period capitalized costs recorded as charge in present period in other operating expenses						94
CAC [Member]
Business Acquisition and Divestitures [Line Items]
Percentage of coinsurance agreement		100.00%
Recognized loss due to difference between market value and book value of funds withheld assets		31
HighMount [Member]
Business Acquisition and Divestitures [Line Items]
Net proceeds from sale of business							787
Repayment of debt		480
Recorded loss on sale		200
Recorded loss on sale, after tax		138
Boardwalk Pipeline [Member]
Business Acquisition and Divestitures [Line Items]
Goodwill recorded		237	215	271
Cash contributed to obtain equity interest in joint venture								269	148
Percentage of equity transferred to acquire equity funds								65.00%	35.00%
Boardwalk Pipeline [Member] | Evangeline Pipeline System [Member]
Business Acquisition and Divestitures [Line Items]
Identifiable finite-lived intangible assets		20
Goodwill recorded		22
Boardwalk Pipeline Partners, LP [Member] | Bluegrass Project [Member]
Business Acquisition and Divestitures [Line Items]
Previous period capitalized costs recorded as charge in present period in other operating expenses						10
Louisiana Midstream LLC [Member]
Business Acquisition and Divestitures [Line Items]
Purchase price received									620
Identifiable finite-lived intangible assets									25
Goodwill recorded									52
Bank loan acquired to fund purchase									225
Boardwalk Pipelines Holding Corporation [Member]
Business Acquisition and Divestitures [Line Items]
Cash contributed to obtain equity interest in joint venture									$ 269
Percentage of equity transferred to acquire equity funds									65.00%