Summary of Significant Accounting Policies - SPPC - Reconciliation of Cash (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 1,392	$ 1,565
Investments and restricted cash and cash equivalents	177	224
Total cash and cash equivalents and restricted cash and cash equivalents	1,586	1,811	$ 1,817	$ 1,244
SPPC
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	17	44
Investments and restricted cash and cash equivalents	7	8
Total cash and cash equivalents and restricted cash and cash equivalents	$ 24	$ 52	$ 56	$ 16