Short-term Debt and Credit Facilities - PAC (Details)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Line of Credit Facility [Line Items]
Credit facilities	$ 11,281,000,000	$ 11,030,000,000
Short-term debt	(2,009,000,000)	(2,286,000,000)
Tax-exempt bond support and letters of credit	(589,000,000)	(590,000,000)
Net credit facilities	8,683,000,000	8,154,000,000
PAC
Line of Credit Facility [Line Items]
Credit facilities	1,200,000,000	1,200,000,000
Short-term debt	0	(93,000,000)
Tax-exempt bond support and letters of credit	(218,000,000)	(218,000,000)
Net credit facilities	982,000,000	889,000,000
Letters of credit outstanding	19,000,000	11,000,000
PAC | Unsecured credit facility, expiring June 2024 | Line of credit
Line of Credit Facility [Line Items]
Credit facilities	$ 1,200,000,000
Debt to capitalization ratio	0.65
PAC | Unsecured credit facility, expiring June 2024 | Commercial paper | Line of credit
Line of Credit Facility [Line Items]
Line of credit, amount drawn	$ 0	$ 93,000,000
Weighted average interest rate		0.16%