Schedule I - Condensed Financial Information - Income and Comprehensive Income (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Income Statements,Captions [Line Items]
Interest expense	$ (1,019)	$ (991)	$ (819)
NET INCOME FOR COMMON STOCK	1,101	1,343	1,382	$ 1,525
Comprehensive Income	$ 1,095	$ 1,340	$ 1,392
Net Income Per Share – Basic (in dollars per share)	$ 3.29	$ 4.09	$ 4.43
Net Income Per Share – Diluted (in dollars per share)	$ 3.28	$ 4.08	$ 4.42
Average Number Of Shares Outstanding—Basic (in shares)	334.8	328.5	311.7
Average Number Of Shares Outstanding—Diluted (in shares)	335.7	329.5	312.9
Parent Company
Condensed Income Statements,Captions [Line Items]
Equity in earnings of subsidiaries	$ 1,105	$ 1,354	$ 1,447
Other income (deductions), net of taxes	56	76	(6)
Interest expense	(60)	(87)	(59)
NET INCOME FOR COMMON STOCK	1,101	1,343	1,382
Comprehensive Income	$ 1,095	$ 1,340	$ 1,392
Net Income Per Share – Basic (in dollars per share)	$ 3.29	$ 4.09	$ 4.43
Net Income Per Share – Diluted (in dollars per share)	3.28	4.08	4.42
Dividends Declared Per Share (in dollars per share)	$ 3.06	$ 2.96	$ 2.86
Average Number Of Shares Outstanding—Basic (in shares)	334.8	328.5	311.1
Average Number Of Shares Outstanding—Diluted (in shares)	335.7	329.5	312.9