Other Material Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2013 Lawsuits	Jan. 31, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2013 Tax deficiency paid in December 2005 [Member]	Jun. 30, 2013 Interest in April 2006 [Member]	Jun. 30, 2013 Leases [Member]	Jun. 30, 2013 Energy [Member]	Jun. 30, 2013 Construction [Member]	Jun. 30, 2013 IRS [Member]
Operating Leased Assets [Line Items]
Number of suits pending against the company	93
Total investment in electric generating and gas distribution facilities	$ 259
Transactions financed with equity	93
Transactions financed with non-recourse	166
Tax deficiency paid to IRS					0.3
Interest paid related to tax deficiency						0.2
Disallowed deduction					574
Estimated charge after-tax			150
Gain from LILO transaction termination	29
Proceeds from the termination of a LILO transaction	108
The company's net investment in LILO transaction	43			(76)
Gross investment in LILO transaction	47			228
Deferred tax liabilities	4			304
Defray of interest charges relating to potential tax liability		447
Returned deposit from IRS	405			70						95
Guarantee obligations maximum exposure	883			859
Guarantees issued							2	25	4
Maximum potential obligation	$ 5