Regulatory Matters - SPPC - Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Regulatory Assets [Line Items]
Total regulatory assets	$ 5,565	$ 5,062
Regulatory assets, current	1,398	1,319
Regulatory assets, noncurrent	4,167	3,743
Regulatory assets not earning a return on investment	3,200	2,300
SPPC
Regulatory Assets [Line Items]
Total regulatory assets	381	611
Regulatory assets, current	161	357
Regulatory assets, noncurrent	220	254
Regulatory assets not earning a return on investment	$ 132	143
SPPC | Natural disaster protection plan
Regulatory Assets [Line Items]
Regulatory asset, amortization period	1 year
Total regulatory assets	$ 78	69
SPPC | Deferred energy costs
Regulatory Assets [Line Items]
Regulatory asset, amortization period	1 year
Total regulatory assets	$ 77	277
SPPC | Merger costs from 1999 merger
Regulatory Assets [Line Items]
Regulatory asset, amortization period	23 years
Total regulatory assets	$ 60	63
SPPC | Employee benefit plans
Regulatory Assets [Line Items]
Regulatory asset, amortization period	8 years
Total regulatory assets	$ 48	57
SPPC | Deferred operating costs
Regulatory Assets [Line Items]
Regulatory asset, amortization period	4 years
Total regulatory assets	$ 25	35
SPPC | Other
Regulatory Assets [Line Items]
Total regulatory assets	$ 93	$ 110