Condensed Parent Company Financial Statements (Condensed Statements of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net cash flows from operating activities	$ 867.0	$ 486.0	$ 582.0
Cash flows from (used for) investing activities:
Dividends from consolidated subsidiaries in excess of equity earnings	(120.0)	(47.0)	(61.0)
Net cash flows from (used for) investing activities	(1,401.0)	(933.0)	(728.0)
Cash flows used for financing activities:
Common stock dividends	(456.0)	(428.0)	(403.0)
Proceeds from issuance of common stock, net	246.0	25.0	28.0
Proceeds from issuance of long-term debt	1,455.0	1,338.0	600.0
Net change in commercial paper	(167.0)	127.0	126.0
Other	3.0	2.0	(13.0)
Net cash flows from (used for) financing activities	573.0	431.0	130.0
Net increase (decrease) in cash, cash equivalents and restricted cash	39.0	(16.0)	(16.0)
Cash, cash equivalents and restricted cash at beginning of period	24.0	40.0	56.0
Cash, cash equivalents and restricted cash at end of period	63.0	24.0	40.0
Supplemental cash flows information:
Interest	(378.0)	(311.0)	(272.0)
Income taxes, net	88.0	(6.0)	(3.0)
Parent Company [Member]
Net cash flows from operating activities	445.0	492.0	494.0
Cash flows from (used for) investing activities:
Capital contributions to consolidated subsidiaries	(325.0)	(530.0)	(295.0)
Net change in notes receivable from and payable to affiliates	(281.0)	369.0	(21.0)
Dividends from consolidated subsidiaries in excess of equity earnings	0.0	0.0	50.0
Net cash flows from (used for) investing activities	(606.0)	(161.0)	(266.0)
Cash flows used for financing activities:
Common stock dividends	(456.0)	(428.0)	(403.0)
Proceeds from issuance of common stock, net	246.0	25.0	28.0
Proceeds from issuance of long-term debt	565.0	0.0	0.0
Net change in commercial paper	(195.0)	73.0	147.0
Other	1.0	(1.0)	0.0
Net cash flows from (used for) financing activities	161.0	(331.0)	(228.0)
Net increase (decrease) in cash, cash equivalents and restricted cash	0.0	0.0	0.0
Cash, cash equivalents and restricted cash at beginning of period	0.0	0.0	0.0
Cash, cash equivalents and restricted cash at end of period	0.0	0.0	0.0
Supplemental cash flows information:
Interest	(27.0)	(6.0)	(1.0)
Income taxes, net	$ 22.0	$ 15.0	$ 4.0