Income Tax - Schedule of Differences on Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred tax liabilities:
Property basis differences	$ 9,446	$ 8,614
Regulatory assets:
Unrecognized pension and other postretirement costs	1,162	1,562
Future income tax	986	947
Environmental remediation costs	333	365
Deferred storm costs	23	75
Other regulatory assets	371	367
Equity investments	363	295
Total deferred tax liabilities	12,684	12,225
Deferred tax assets:
Accrued pension and other postretirement costs	581	982
Regulatory liabilities	822	836
Superfund and other environmental costs	304	308
Asset retirement obligations	99	97
Loss carryforwards	59	29
Tax credits carryforward	498	258
Valuation allowance	(16)	(15)
Other	303	362
Total deferred tax assets	2,650	2,857
Net deferred tax liabilities	10,034	9,368
Unamortized investment tax credits	171	169
Net deferred tax liabilities and unamortized investment tax credits	10,205	9,537
CECONY
Deferred tax liabilities:
Property basis differences	8,620	7,922
Regulatory assets:
Unrecognized pension and other postretirement costs	1,104	1,490
Future income tax	940	899
Environmental remediation costs	287	322
Deferred storm costs	1	45
Other regulatory assets	321	308
Equity investments	0	0
Total deferred tax liabilities	11,273	10,986
Deferred tax assets:
Accrued pension and other postretirement costs	467	857
Regulatory liabilities	728	752
Superfund and other environmental costs	265	268
Asset retirement obligations	92	94
Loss carryforwards	0	0
Tax credits carryforward	0	1
Valuation allowance	0	0
Other	312	292
Total deferred tax assets	1,864	2,264
Net deferred tax liabilities	9,409	8,722
Unamortized investment tax credits	41	33
Net deferred tax liabilities and unamortized investment tax credits	$ 9,450	$ 8,755