Short-Term Borrowings (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Amount outstanding at period end	$ 137	$ 137	$ 250
Money Pool
Short-term Debt [Line Items]
Borrowing limit	100	100	100	$ 100
Amount outstanding at period end	91	91	0	0
Average amount outstanding	100	51	43	8
Maximum amount outstanding	$ 100	$ 100	$ 100	$ 100
Weighted average interest rate, computed on a daily basis (percentage)	0.05%	0.05%	0.54%	2.42%
Line of Credit Facility, Interest Rate at Period End	0.05%	0.05%
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	$ 500	$ 500	$ 500	$ 400
Amount outstanding at period end	137	137	250	0
Average amount outstanding	69	63	44	72
Maximum amount outstanding	$ 137	$ 342	$ 250	$ 316
Weighted average interest rate, computed on a daily basis (percentage)	0.17%	0.21%	1.11%	2.68%
Weighted average interest rate at period end (percentage)	0.26%	0.26%	0.29%