Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Property, Plant, and Equipment [Line Items]
Outstanding checks in excess of bank account balances	$ 365	$ 388
Furniture And Equipment [Member] | Minimum [Member]
Property, Plant, and Equipment [Line Items]
Useful life of assets	3 years
Furniture And Equipment [Member] | Maximum [Member]
Property, Plant, and Equipment [Line Items]
Useful life of assets	15 years
Buildings [Member] | Maximum [Member]
Property, Plant, and Equipment [Line Items]
Useful life of assets	40 years
Gathering Facilities [Member] | Maximum [Member]
Property, Plant, and Equipment [Line Items]
Useful life of assets	47 years