Regulatory Matters - NPC - Regulatory Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Total regulatory assets	$ 3,963	$ 3,440
Regulatory assets, current	544	283
Regulatory assets, noncurrent	3,419	3,157
Regulatory assets not earning a return on investment	1,800	1,600
Unrealized loss on derivative contracts
Regulatory Assets [Line Items]
Total regulatory assets	$ 157	31
Deferred operating costs
Regulatory Assets [Line Items]
Regulatory asset, amortization period	9 years
Total regulatory assets	$ 103	124
Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory asset, amortization period	14 years
Total regulatory assets	$ 742	640
NPC
Regulatory Assets [Line Items]
Total regulatory assets	1,019	794
Regulatory assets, current	291	48
Regulatory assets, noncurrent	728	746
Regulatory assets not earning a return on investment	$ 371	288
NPC | Deferred energy costs
Regulatory Assets [Line Items]
Regulatory asset, amortization period	1 year
Total regulatory assets	$ 273	39
NPC | Decommissioning costs
Regulatory Assets [Line Items]
Regulatory asset, amortization period	2 years
Total regulatory assets	$ 169	230
NPC | Unrealized loss on derivative contracts
Regulatory Assets [Line Items]
Regulatory asset, amortization period	1 year
Total regulatory assets	$ 117	11
NPC | Merger costs from 1999 merger
Regulatory Assets [Line Items]
Regulatory asset, amortization period	23 years
Total regulatory assets	$ 110	115
NPC | Deferred operating costs
Regulatory Assets [Line Items]
Regulatory asset, amortization period	12 years
Total regulatory assets	$ 93	119
NPC | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory asset, amortization period	6 years
Total regulatory assets	$ 73	70
NPC | ON Line deferrals
Regulatory Assets [Line Items]
Regulatory asset, amortization period	32 years
Total regulatory assets	$ 42	43
NPC | Legacy Meters
Regulatory Assets [Line Items]
Regulatory asset, amortization period	11 years
Total regulatory assets	$ 41	45
NPC | Employee benefit plans
Regulatory Assets [Line Items]
Regulatory asset, amortization period	8 years
Total regulatory assets	$ 11	50
NPC | Other
Regulatory Assets [Line Items]
Total regulatory assets	$ 90	$ 72