Schedule I - Condensed Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current Assets
Cash and temporary cash investments	$ 1,272	$ 981
Accounts receivable - customers, less allowance for uncollectible accounts	1,701	1,236
Taxes receivable	26	20
Prepayments	271	260
Other current assets	231	200
TOTAL CURRENT ASSETS	5,301	4,272
Investments in subsidiaries and others	1,816	2,065
Goodwill	446	446
Other noncurrent assets	9,223	7,853
TOTAL ASSETS	62,895	58,079	$ 53,920
Current Liabilities
Long-term debt due within one year		1,446
Term Loan	165	0
Notes payable	1,705	1,692
Accounts payable	1,475	1,164
Accrued taxes	150	76
Other current liabilities	426	371
TOTAL CURRENT LIABILITIES	7,354	6,287
Long-term debt	20,382	18,527
Shareholders’ Equity
Equity	18,847	18,022
TOTAL LIABILITIES AND EQUITY	62,895	58,079
Parent Company
Current Assets
Cash and temporary cash investments	144	2
Accounts receivable - customers, less allowance for uncollectible accounts	1
Taxes receivable	18	18
Term loan receivable from affiliated companies	0	0
Accounts receivable from affiliated companies	1,256	870
Prepayments	62	32
Other current assets	12	12
TOTAL CURRENT ASSETS	1,493	934
Investments in subsidiaries and others	18,670	18,009
Goodwill	406	406
Deferred income tax	55	14
Long-term debt receivable from affiliated companies	875	1,275
Other noncurrent assets	0	0
TOTAL ASSETS	21,499	20,638
Current Liabilities
Long-term debt due within one year	1,178	3
Term Loan	0	0
Notes payable	0	537
Accounts payable	0	0
Accounts payable to affiliated companies	517	595
Accrued taxes	6	2
Other current liabilities	12	10
TOTAL CURRENT LIABILITIES	1,713	1,147
Deferred income tax	0	0
Total Liabilities	1,713	1,147
Long-term debt	939	1,469
Shareholders’ Equity
Common stock, including additional paid-in capital	8,844	8,089
Retained earnings	10,003	9,933
Equity	18,847	18,022
TOTAL LIABILITIES AND EQUITY	$ 21,499	$ 20,638