SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF PARENT - CASH FLOWS (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Condensed Cash Flow Statements, Captions [Line Items]
Net cash used in operating activities	$ 3,088	$ 3,516	$ 3,625
Expenditures for property, plant and equipment	(3,708)	(3,544)	(3,705)
Expenditures for acquisition	0	(9,568)	(147)
Other	30	41	24
Net cash used in investing activities	(4,593)	(12,470)	(4,885)
Common stock dividends paid	(993)	(877)	(755)
Preferred dividends paid	(142)	(89)	0
Issuances of mandatory convertible preferred stock, net	0	2,258	0
Issuances of common stock, net	1,830	2,272	47
Repurchases of common stock	(26)	(21)	(15)
Issuances of long-term debt	4,296	8,927	4,260
Payments on long-term debt	(3,667)	(3,342)	(2,587)
Increase (decrease) in loans from affiliates, net	3	3	9
Increase (decrease) in loans from affiliates, net	(16)	(95)	(505)
Net cash provided by financing activities	1,475	8,850	1,192
Cash and cash equivalents, January 1	102
Cash and cash equivalents, December 31	108	102
SUPPLEMENTAL DISCLOSURE OF NONCASH FINANCING ACTIVITIES
Common dividends issued in stock	55	54	53
Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash used in operating activities	294	213	89
Expenditures for property, plant and equipment	(8)	(11)	(11)
Expenditures for acquisition	0	(329)	0
Capital contributions to investees	(1,528)	(9,457)	0
Decrease in loans to affiliate, net	0	(1)	0
Expenditures for Merger-related costs	0	0	(12)
Other	4	0	0
Net cash used in investing activities	(1,532)	(9,798)	(23)
Common stock dividends paid	(993)	(877)	(755)
Preferred dividends paid	(142)	(89)	0
Issuances of mandatory convertible preferred stock, net	0	2,258	0
Issuances of common stock, net	1,830	2,272	47
Repurchases of common stock	(26)	(21)	(15)
Issuances of long-term debt	758	4,969	1,595
Payments on long-term debt	(1,500)	(500)	(600)
Increase (decrease) in loans from affiliates, net	1,328	1,520
Increase (decrease) in loans from affiliates, net			(239)
Payments of Debt Issuance Costs	(25)	(37)	(7)
Net cash provided by financing activities	1,230	9,495	26
(Decrease) increase in cash and cash equivalents	(8)	(90)	92
Cash and cash equivalents, January 1	14	104	12
Cash and cash equivalents, December 31	6	14	104
SUPPLEMENTAL DISCLOSURE OF NONCASH FINANCING ACTIVITIES
Accrued Merger-related transaction costs	0	0	31
Preferred dividends declared but not paid	36	36	0
Common dividends issued in stock	55	54	53
Common dividends declared but not paid	$ 283	$ 245	$ 207