SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF PARENT - CASH FLOWS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	$ 2,591	$ 3,088	$ 3,516
Expenditures for property, plant and equipment	(4,676)	(3,708)	(3,544)
Expenditures for acquisition	0	0	(9,568)
Distributions from investments	651	247	202
Other	15	21	31
Net cash provided by (used in) investing activities	553	(4,593)	(12,470)
Common stock dividends paid	(1,174)	(993)	(877)
Preferred dividends paid	(157)	(142)	(89)
Proceeds from Issuance of Preferred Stock and Preference Stock	891	0	2,258
Issuances of common stock, net	11	1,830	2,272
Repurchases of common stock	(566)	(26)	(21)
Issuances of long-term debt	6,051	4,296	8,927
Payments on long-term debt	(5,864)	(3,667)	(3,342)
Increase in loans from affiliates, net	7	3	3
Net cash (used in) provided by financing activities	(2,373)	1,475	8,850
Cash and cash equivalents, January 1	108
Cash and cash equivalents, December 31	960	108
SUPPLEMENTAL DISCLOSURE OF NONCASH FINANCING ACTIVITIES
Common dividends issued in stock	22	55	54
Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	(978)	294	213
Expenditures for property, plant and equipment	(9)	(8)	(11)
Expenditures for acquisition	0	0	(329)
Capital contributions to investees	(364)	(1,528)	(9,457)
Distributions from investments	3,616	0	0
Decrease (increase) in loans to affiliates, net	2	0	(1)
Other	0	4	0
Net cash provided by (used in) investing activities	3,245	(1,532)	(9,798)
Common stock dividends paid	(1,174)	(993)	(877)
Preferred dividends paid	(157)	(142)	(89)
Proceeds from Issuance of Preferred Stock and Preference Stock	891	0	2,258
Issuances of common stock, net	11	1,830	2,272
Repurchases of common stock	(566)	(26)	(21)
Issuances of long-term debt	1,599	758	4,969
Payments on long-term debt	(3,700)	(1,500)	(500)
Increase in loans from affiliates, net	1,194	1,328	1,520
Equity transaction costs with third parties	(4)	0	0
Debt issuance costs	(1)	(25)	(37)
Net cash (used in) provided by financing activities	(1,907)	1,230	9,495
Increase (decrease) in cash and cash equivalents	360	(8)	(90)
Cash and cash equivalents, January 1	6	14	104
Cash and cash equivalents, December 31	366	6	14
SUPPLEMENTAL DISCLOSURE OF NONCASH FINANCING ACTIVITIES
Preferred dividends declared but not paid	47	36	36
Common dividends issued in stock	22	55	54
Common dividends declared but not paid	$ 301	$ 283	$ 245