Investment in Transmission Affiliates - ATC Summarized Financial Data (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Investment in transmission affiliates
Operating revenues	$ 8,893.0	$ 9,597.4	$ 8,316.0
Operating expenses	6,985.0	7,673.2	6,601.1
Other expense, net	371.7	191.6	216.1
Current assets	2,795.7	3,187.7
Assets, Noncurrent	41,144.0	38,684.4
Total assets	43,939.7	41,872.1	38,988.5
Current liabilities	5,114.8	4,611.0
Long-term debt	15,366.9	14,655.7
Other noncurrent liabilities	659.3	660.6
Total liabilities and equity	43,939.7	41,872.1
ATC
Investment in transmission affiliates
Operating revenues	818.9	751.2	754.8
Operating expenses	407.6	381.5	376.2
Other expense, net	131.7	123.0	113.9
Net income	279.6	246.7	$ 264.7
Current assets	115.2	89.6
Assets, Noncurrent	6,337.0	5,997.8
Total assets	6,452.2	6,087.4
Current liabilities	495.9	511.9
Long-term debt	2,736.0	2,613.0
Other noncurrent liabilities	585.2	485.8
Members' equity	2,635.1	2,476.7
Total liabilities and equity	$ 6,452.2	$ 6,087.4