Short-term Debt and Credit Facilities - PAC (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Feb. 21, 2025	Dec. 31, 2023
Line of Credit Facility [Line Items]
Credit facilities	$ 11,596		$ 10,705
Short-term debt	(1,123)		(4,148)
Tax-exempt bond support and letters of credit	(325)		(556)
Net credit facilities	10,148		6,001
PAC
Line of Credit Facility [Line Items]
Credit facilities	2,900		2,000
Short-term debt	(240)		(1,604)
Tax-exempt bond support and letters of credit	(52)		(249)
Net credit facilities	$ 2,608		$ 147
Weighted average interest rate	4.65%		6.16%
Letters of credit outstanding	$ 34		$ 168
PAC | Line of credit
Line of Credit Facility [Line Items]
Debt to capitalization ratio	0.57
PAC | Line of credit | Maximum
Line of Credit Facility [Line Items]
Debt to capitalization ratio	0.65
PAC | Letter of credit
Line of Credit Facility [Line Items]
Credit facilities	$ 488
PAC | Letter of credit | Subsequent event
Line of Credit Facility [Line Items]
Credit facilities		$ 713
Additional line of credit		225
PAC | Unsecured credit facility, expiring June 2025 | Line of credit
Line of Credit Facility [Line Items]
Credit facilities	$ 900
Debt instrument, term	364 days
PAC | Unsecured credit facility, expiring June 2027
Line of Credit Facility [Line Items]
Letters of credit outstanding	$ 0		31
PAC | Unsecured credit facility, expiring June 2027 | Line of credit
Line of Credit Facility [Line Items]
Credit facilities	2,000
Line of credit outstanding	55
PAC | Unsecured credit facility, expiring June 2027 | Line of credit | Subsequent event
Line of Credit Facility [Line Items]
Credit facilities		$ 2,000
PAC | Unsecured credit facility, expiring June 2027 | Letter of credit
Line of Credit Facility [Line Items]
Credit facilities	$ 255		$ 255