Leases - Schedule of Leveraged Lease Transactions Effect on Consolidated Income Statement (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Guarantor Obligations [Line Items]
Total decrease in net income	$ (95)
Decrease to Non-Utility Operating Revenues [Member]
Guarantor Obligations [Line Items]
Total decrease in net income	(27)
Increase to Other Interest Expense [Member]
Guarantor Obligations [Line Items]
Total decrease in net income	(131)
Income Tax Benefit [Member]
Guarantor Obligations [Line Items]
Total decrease in net income	$ 63