Schedule I - Condensed Financial Information - Income and Comprehensive Income (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Income Statements,Captions [Line Items]
Interest expense	$ (819)	$ (729)	$ (696)
NET INCOME	1,382	1,525	1,245
Comprehensive Income	$ 1,392	$ 1,526	$ 1,252
Net Income Per Share – Basic (in dollars per share)	$ 4.43	$ 4.97	$ 4.15
Net Income Per Share – Diluted (in dollars per share)	$ 4.42	$ 4.94	$ 4.12
Average Number Of Shares Outstanding—Basic (in shares)	311.7	307.1	300.4
Average Number Of Shares Outstanding—Diluted (in shares)	312.9	308.8	301.9
Parent Company
Condensed Income Statements,Captions [Line Items]
Equity in earnings of subsidiaries	$ 1,447	$ 1,544	$ 1,254
Other income (deductions), net of taxes	(6)	31	32
Interest expense	(59)	(50)	(41)
NET INCOME	1,382	1,525	1,245
Comprehensive Income	$ 1,392	$ 1,526	$ 1,252
Net Income Per Share – Basic (in dollars per share)	$ 4.43	$ 4.97	$ 4.15
Net Income Per Share – Diluted (in dollars per share)	4.42	4.94	4.12
Dividends Declared Per Share (in dollars per share)	$ 2.86	$ 2.76	$ 2.68
Average Number Of Shares Outstanding—Basic (in shares)	311.7	307.1	300.4
Average Number Of Shares Outstanding—Diluted (in shares)	312.9	308.8	301.9