Schedule I - Condensed Financial Information Of Parent (Statement of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net cash flows provided by operating activities	$ 2,170	$ 2,170	$ 2,118
Cash Flows From Investing Activities:
Other	3	18	7
Net cash flows provided by (used in) investing activities	(2,435)	(2,336)	(2,204)
Cash flows from financing activities:
Dividends on common stock	(472)	(451)	(431)
Short-term debt, net	(157)	112	(74)
Issuances of long-term debt	1,527	1,352	1,345
Issuances of common stock	68	74	0
Repurchases of common stock for stock-based compensation	0	0	(24)
Employee payroll taxes related to stock-based compensation	(29)	(19)	(15)
Debt issuance costs	17	14	11
Net cash flows used in financing activities	334	205	102
Net change in cash, cash equivalents, and restricted cash	69	39	16
Cash, cash equivalents, and restricted cash at beginning of year	107	68	52
Cash, cash equivalents, and restricted cash at end of year	176	107	68
Noncash financing activity - Issuance of common stock for stock-based compensation	54	35	0
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net cash flows provided by operating activities	491	550	454
Cash Flows From Investing Activities:
Money pool advances, net	(26)	(63)	14
Notes receivable – ATXI, net	0	0	275
Investments in subsidiaries	(142)	(208)	(151)
Other	5	5	6
Net cash flows provided by (used in) investing activities	(163)	(266)	144
Cash flows from financing activities:
Dividends on common stock	(472)	(451)	(431)
Short-term debt, net	(317)	87	(124)
Money pool borrowings, net	(22)	18	(5)
Issuances of long-term debt	450	0	0
Issuances of common stock	68	74	0
Repurchases of common stock for stock-based compensation	0	0	(24)
Employee payroll taxes related to stock-based compensation	(29)	(19)	(15)
Debt issuance costs	4	0	0
Net cash flows used in financing activities	(326)	(291)	(599)
Net change in cash, cash equivalents, and restricted cash	2	(7)	(1)
Cash, cash equivalents, and restricted cash at beginning of year	1	8	9
Cash, cash equivalents, and restricted cash at end of year	3	1	8
Cash dividends received from consolidated subsidiaries	445	450	362
Noncash financing activity - Issuance of common stock for stock-based compensation	$ 54	$ 35	$ 0

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