Variable Interest Entities - Schedule of Assets and Liabilities Included in Consolidated Balance Sheet (Detail) (OCI Solar San Antonio [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Variable Interest Entity [Line Items]
Assets	$ 136
Liabilities	78
Restricted Cash [Member]
Variable Interest Entity [Line Items]
Assets	13
Non-utility Property, less Accumulated Depreciation [Member]
Variable Interest Entity [Line Items]
Assets	111
Other Assets [Member]
Variable Interest Entity [Line Items]
Assets	12
Long-term Debt Due within One Year [Member]
Variable Interest Entity [Line Items]
Liabilities	66
Other Liabilities [Member]
Variable Interest Entity [Line Items]
Liabilities	$ 12