Schedule I - Condensed Financial Information Of Parent (Statement of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	$ 2,170	$ 2,118	$ 2,117
Cash Flows From Investing Activities:
Other	18	7	(9)
Net Cash Provided by (Used in) Investing Activities	(2,336)	(2,204)	(2,158)
Cash flows from financing activities:
Dividends on common stock	(451)	(431)	(416)
Short-term debt, net	112	(74)	257
Proceeds from Issuance of Common Stock	74	0	0
Issuances of Long-term debt	1,352	1,345	396
Capital issuance costs	(14)	(11)	(9)
Payments for Repurchase of Common Stock	0	(24)	(51)
Share-based payments	(19)	(15)	(32)
Net cash provided by (used in) financing activities	205	102	(258)
Net change in cash and cash equivalents	39	16	(299)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	107	68	52	$ 351
Stock Issued	35
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	550	454	483
Cash Flows From Investing Activities:
Money pool advances, net	(63)	14	(27)
Intercompany notes receivable, net		275	(60)
Investments in subsidiaries	(208)	(151)	(123)
Other	5	6	2
Net Cash Provided by (Used in) Investing Activities	(266)	144	(208)
Cash flows from financing activities:
Dividends on common stock	(451)	(431)	(416)
Short-term debt, net	87	(124)	206
Money pool borrowings, net	18	(5)	19
Proceeds from Issuance of Common Stock	74		0
Payments for Repurchase of Common Stock	0	(24)	(51)
Share-based payments	(19)	(15)	(32)
Net cash provided by (used in) financing activities	(291)	(599)	(274)
Net change in cash and cash equivalents	(7)	(1)	1
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1	8	9	$ 8
Cash dividends received from consolidated subsidiaries	450	$ 362	$ 465
Stock Issued	$ 35