Capitalization - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Consolidated Edison Inc
Fair values of long-term debt	$ 13,310	$ 12,744
Consolidated Edison Inc | Level 2 [Member]
Fair values of long-term debt	12,674
Consolidated Edison Inc | Level 3 [Member]
Fair values of long-term debt	636
CECONY
Fair values of long-term debt	12,135	11,593
CECONY | Level 2 [Member]
Fair values of long-term debt	11,499
CECONY | Level 3 [Member]
Fair values of long-term debt	$ 636