Derivative Instruments - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2014 Mcf	Dec. 31, 2013 Mcf
Revolving Credit Facility [Member] | Revolving Credit Facility 1 [Member]
Derivative [Line Items]
Five billion dollar facility	$ 5,000,000,000
Securing most derivative counterparties [Member] | Revolving Credit Facility [Member] | Revolving Credit Facility 1 [Member]
Derivative [Line Items]
Five billion dollar facility	5,000,000,000
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gross derivative liability	(1,085,000,000)	(986,000,000)
Aggregate fair value of derivative instruments with credit-risk-related contingent features for which a net liability position existed, net of collateral	77,000,000	42,000,000
Not Designated as Hedging Instrument [Member] | Permitted to Offset Gross Derivative Asset with Financial Institutions [Member]
Derivative [Line Items]
Gross derivative liability	$ (73,000,000)	$ (76,000,000)
Commodity [Member] | Natural Gas [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Financial derivative transactions	1,000,000	16,000,000