Schedule I - Condensed Financial Information - Income and Comprehensive Income (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Income Statements,Captions [Line Items]
Interest expense	$ (991)	$ (819)	$ (729)
NET INCOME FOR COMMON STOCK	1,343	1,382	1,525
Comprehensive Income	$ 1,340	$ 1,392	$ 1,526
Net Income Per Share – Basic (in dollars per share)	$ 4.09	$ 4.43	$ 4.97
Net Income Per Share – Diluted (in dollars per share)	$ 4.08	$ 4.42	$ 4.94
Average Number Of Shares Outstanding—Basic (in shares)	328.5	311.7	307.1
Average Number Of Shares Outstanding—Diluted (in shares)	329.5	312.9	308.8
Parent Company
Condensed Income Statements,Captions [Line Items]
Equity in earnings of subsidiaries	$ 1,354	$ 1,447	$ 1,544
Other income (deductions), net of taxes	76	(6)	31
Interest expense	(87)	(59)	(50)
NET INCOME FOR COMMON STOCK	1,343	1,382	1,525
Comprehensive Income	$ 1,340	$ 1,392	$ 1,526
Net Income Per Share – Basic (in dollars per share)	$ 4.09	$ 4.43	$ 4.97
Net Income Per Share – Diluted (in dollars per share)	4.08	4.42	4.94
Dividends Declared Per Share (in dollars per share)	$ 2.96	$ 2.86	$ 2.76
Average Number Of Shares Outstanding—Basic (in shares)	328.5	311.1	307.1
Average Number Of Shares Outstanding—Diluted (in shares)	329.5	312.9	308.8