Leases - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended			12 Months Ended
	Aug. 31, 2013	Jun. 30, 2013	Jan. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Operating Leased Assets [Line Items]
Accumulated amortization				$ 1.0	$ 1.0
Lease In/Lease Out total investment				259
Lease In/Lease Out total financed by equity				93
Lease In/Lease Out total financed by long-term debt				166
Company's net investment in LILO transactions				0	(76)
Gross investment in leverage leases					228
Deferred tax liabilities					304
Estimated charge after-tax			150
Gain from LILO transaction termination	26	29
Proceeds from the termination of a LILO transaction	92	108
Defray of interest charges relating to potential tax liability			447
Returned deposit from IRS				327	70
Settlement of federal and state tax liabilities				48
Refund from IFRS				10
IRS [Member]
Operating Leased Assets [Line Items]
Returned deposit from IRS				125
Settlement of tax and interest				38
Tax deficiency paid in December 2005 [Member]
Operating Leased Assets [Line Items]
Tax deficiency paid to IRS				0.3
Interest in April 2006 [Member]
Operating Leased Assets [Line Items]
Interest paid related to tax deficiency				0.2
Disallowance of Tax 1998 to 2011 [Member]
Operating Leased Assets [Line Items]
Disallowed deduction				574
CECONY [Member]
Operating Leased Assets [Line Items]
Accumulated amortization				0.6	0.4
Returned deposit from IRS				$ 86	$ 65