Schedule I - Condensed Financial Information Of Parent (Balance Sheet) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets:
Cash and cash equivalents	$ 16	$ 16
Miscellaneous accounts and notes receivable	63	79
Other current assets	118	63
Total current assets	1,431	1,533
Accumulated deferred income taxes, net	0	9
Other assets	876	650
Total assets	28,933	27,215
Liabilities and Shareholders' Equity:
Current maturities of long-term debt	442	580
Short-term debt	440	597
Other current liabilities	585	544
Total current liabilities	2,505	2,687
Long-term debt	8,915	7,859
Pension and other postretirement benefits	401	558
Other deferred credits and liabilities	467	408
Commitments and Contingencies (Note 5)
Retained earnings	2,380	2,024
Accumulated other comprehensive loss	(17)	(22)
Total shareholders' equity	8,201	7,773	$ 7,326
Total liabilities and shareholders' equity	$ 28,933	$ 27,215
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000	400,000,000
Common Stock, Shares, Outstanding	246,200,000	244,500,000	242,600,000	242,600,000
Parent Company
Assets:
Cash and cash equivalents	$ 0	$ 0
Advances to money pool	102	76
Accounts receivable – affiliates	73	43
Miscellaneous accounts and notes receivable	4	2
Other current assets	3	2
Total current assets	182	123
Investments in subsidiaries	9,108	8,559
Note receivable – ATXI	75	75
Accumulated deferred income taxes, net	49	108
Other assets	145	126
Total assets	9,559	8,991
Liabilities and Shareholders' Equity:
Current maturities of long-term debt	350	0
Short-term debt	153	470
Borrowings from money pool	24	46
Accounts payable – affiliates	39	10
Other current liabilities	23	12
Total current liabilities	589	538
Long-term debt	794	697
Pension and other postretirement benefits	37	43
Other deferred credits and liabilities	80	82
Total liabilities	1,500	1,360
Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 246.2 and 244.5, respectively	2	2
Other paid-in capital, principally premium on common stock	5,694	5,627
Retained earnings	2,380	2,024
Accumulated other comprehensive loss	(17)	(22)
Total shareholders' equity	8,059	7,631
Total liabilities and shareholders' equity	$ 9,559	$ 8,991
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000	400,000,000
Common Stock, Shares, Outstanding	246,200,000	244,500,000