Retirement Benefits - Fair Value Measurements of Pension and Postretirement Benefit Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Derivative, Fair Value, Net	$ 2	$ 2
Derivative, Notional Amount	6,879	6,668
Net liabilities pending transactions excluded	132	120
Nuclear Decommissioning Trust Fund Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Derivative, Notional Amount	104	99
Financial Instruments Sold, Not yet Purchased, Corporate Debt	(62)	(48)
Nuclear Decommissioning Trust Fund Investments [Member] | Exelon Generation Co L L C [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Derivative, Notional Amount	104	99
Financial Instruments Sold, Not yet Purchased, Corporate Debt	(62)	(48)
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	20,344	18,590	$ 16,678
Financial Instruments Sold, Not yet Purchased, Corporate Debt	(96)	(75)
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	20,476	18,710
Alternative Investment	8,161	7,916
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,800	5,168
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,685	5,139
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	830	487
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	529	365
Alternative Investment	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	408	258
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	121	107
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	6,809	6,211
Alternative Investment	2,552	2,589
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	4,255	3,616
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	1
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2	5
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,504	1,574
Alternative Investment	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,137	1,294
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	367	280
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	85	56
Alternative Investment	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	85	56
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,446	4,635
Alternative Investment	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	4,873	4,390
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	573	245
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	797	1,156
Alternative Investment	537	851
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	239	305
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	21	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	7,832	7,421
Alternative Investment	537	851
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,137	1,294
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,564	5,031
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	594	245
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,632	1,391
Alternative Investment	1,632	1,391
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,314	1,126
Alternative Investment	1,314	1,126
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,080	1,030
Alternative Investment	1,080	1,030
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,280	1,166
Alternative Investment	1,046	929
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	234	237
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2,554	2,541	2,408
Financial Instruments Sold, Not yet Purchased, Corporate Debt	(42)	(35)
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2,554	2,541
Alternative Investment	1,284	1,453
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	969	787
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	301	301
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	102	88
Alternative Investment	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	50	39
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	52	49
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,189	1,197
Alternative Investment	569	719
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	618	473
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2	5
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	82	81
Alternative Investment	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	16	17
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	66	64
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	89	107
Alternative Investment	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	89	107
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	89	71
Alternative Investment	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	89	71
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	467	464
Alternative Investment	179	201
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	285	258
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3	5
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	727	723
Alternative Investment	179	201
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	301	275
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	247	247
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	308	293
Alternative Investment	308	293
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	111	109
Alternative Investment	111	109
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	117	131
Alternative Investment	117	131
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension and other post retirement benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Derivative, Notional Amount	239	632
Pension and other post retirement benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	830	487	486
Pension and other post retirement benefit [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2	5	2
Pension and other post retirement benefit [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	594	245	216
Pension and other post retirement benefit [Member] | Private Placement [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	234	237	$ 268
Pension and other post retirement benefit [Member] | Fair Value, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	23,030	21,251
Alternative Investment	9,445	9,369
Pension and other post retirement benefit [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	6,769	5,955
Pension and other post retirement benefit [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,986	5,440
Pension and other post retirement benefit [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 830	$ 487