Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Furniture And Equipment [Member] Minimum [Member]	Dec. 31, 2013 Furniture And Equipment [Member] Maximum [Member]	Dec. 31, 2013 Buildings [Member] Maximum [Member]	Dec. 31, 2013 Gathering Facilities [Member] Maximum [Member]
Property, Plant, and Equipment [Line Items]
Useful life of assets			3 years	15 years	40 years	47 years
Outstanding checks in excess of bank account balances	$ 326	$ 339