Pension Benefits - Total Periodic Benefit Costs (Details) - Pension Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	$ 275	$ 297	$ 227
Interest cost on projected benefit obligation	596	575	572
Expected return on plan assets	(947)	(886)	(832)
Recognition of net actuarial loss	596	775	618
Recognition of prior service costs	4	4	4
NET PERIODIC BENEFIT COST	524	765	589
Amortization of regulatory asset	0	1	2
TOTAL PERIODIC BENEFIT COST	524	766	591
Cost capitalized	(214)	(301)	(225)
Reconciliation to rate level	54	(74)	118
Cost charged to operating expenses	364	391	484
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	258	279	211
Interest cost on projected benefit obligation	559	538	536
Expected return on plan assets	(898)	(840)	(789)
Recognition of net actuarial loss	565	734	586
Recognition of prior service costs	2	2	2
NET PERIODIC BENEFIT COST	486	713	546
Amortization of regulatory asset	0	1	2
TOTAL PERIODIC BENEFIT COST	486	714	548
Cost capitalized	(203)	(285)	(212)
Reconciliation to rate level	58	(74)	108
Cost charged to operating expenses	$ 341	355	444
Increase in CECONY's pension obligation		$ 45	$ 45