Investment in Transmission Affiliates - ATC Summarized Financial Data (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Investment in transmission affiliates
Operating revenues	$ 8,599.9	$ 8,893.0	$ 9,597.4
Operating expenses	6,447.1	6,985.0	7,673.2
Other expense, net	406.5	371.7	191.6
Current assets	2,911.7	2,795.7
Noncurrent assets	44,451.5	41,144.0
Total assets	47,363.2	43,939.7	41,872.1
Current liabilities	4,841.9	5,114.8
Long-term debt	17,178.1	15,366.9
Other noncurrent liabilities	838.1	835.3
Total liabilities and equity	47,363.2	43,939.7
ATC
Investment in transmission affiliates
Operating revenues	911.3	818.9	751.2
Operating expenses	442.4	407.6	381.5
Other expense, net	137.7	131.7	123.0
Net income	331.2	279.6	$ 246.7
Current assets	126.6	115.2
Noncurrent assets	6,792.6	6,337.0
Total assets	6,919.2	6,452.2
Current liabilities	482.4	495.9
Long-term debt	3,083.4	2,736.0
Other noncurrent liabilities	545.0	585.2
Members' equity	2,808.4	2,635.1
Total liabilities and equity	$ 6,919.2	$ 6,452.2