Fresh Start Accounting (Fresh Start - Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Apr. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 1,125	$ 322
Total current assets	2,781	2,597
Property, plant and equipment, net	13,933	11,850
Total assets	20,693	18,624
LIABILITIES AND EQUITY (DEFICIT)
Long-term debt due within one year	15	15
Accounts payable	857	1,200
Accrued other taxes	118	137
Other current liabilities	693	396
Total current liabilities	2,275	2,295
Deferred income taxes	643	558	$ 291
Other liabilities	553	483
Liabilities subject to compromise				$ 11,565
Total liabilities	15,414	13,490
Equity (Deficit):
Common stock	2	2
Retained earnings (deficit)	884	855
Accumulated other comprehensive income (loss), net of tax	96	79
Total equity	5,279	5,134	4,108
Total liabilities and equity	$ 20,693	$ 18,624
Predecessor [Member]
Current assets:
Cash and cash equivalents			2,059
Accounts receivable, net			516
Contract acquisition costs			91
Prepaid expenses			92
Income taxes and other current assets			45
Total current assets			2,803
Property, plant and equipment, net			13,020
Other intangibles, net			578
Other assets			526
Total assets			16,927
LIABILITIES AND EQUITY (DEFICIT)
Long-term debt due within one year			5,782
Accounts payable			518
Advanced billings			208
Accrued other taxes			185
Accrued interest			81
Pension and other postretirement benefits			48
Other current liabilities			309
Total current liabilities			7,131
Deferred income taxes			389
Pension and other postretirement benefits			2,163
Other liabilities			440
Total liabilities not subject to compromise			10,123
Liabilities subject to compromise			11,570
Total liabilities			21,693
Equity (Deficit):
Common stock			27
Additional paid-in capital			4,818
Retained earnings (deficit)			(8,855)
Accumulated other comprehensive income (loss), net of tax			(741)
Treasury common stock			(15)
Total equity			(4,766)
Total liabilities and equity			16,927
Successor [Member]
Current assets:
Cash and cash equivalents			890
Accounts receivable, net			516
Prepaid expenses			92
Income taxes and other current assets			42
Total current assets			1,540
Property, plant and equipment, net			8,547
Other intangibles, net			4,441
Other assets			398
Total assets			14,926
LIABILITIES AND EQUITY (DEFICIT)
Long-term debt due within one year			15
Accounts payable			512
Advanced billings			208
Accrued other taxes			185
Accrued interest			80
Pension and other postretirement benefits			48
Other current liabilities			326
Total current liabilities			1,374
Deferred income taxes			291
Pension and other postretirement benefits			1,726
Other liabilities			412
Principal outstanding			7,015
Total liabilities not subject to compromise			10,818
Total liabilities			10,818
Equity (Deficit):
Common stock			2
Additional paid-in capital			4,106
Total equity			4,108
Total liabilities and equity			14,926
Reorganization Adjustments [Member]
Current assets:
Cash and cash equivalents			(1,169)
Total current assets			(1,169)
Other assets			(8)
Total assets			(1,177)
LIABILITIES AND EQUITY (DEFICIT)
Long-term debt due within one year			(5,767)
Accounts payable			(6)
Accrued interest			(1)
Other current liabilities			53
Total current liabilities			(5,721)
Deferred income taxes			70
Principal outstanding			6,738
Total liabilities not subject to compromise			1,087
Liabilities subject to compromise			(11,570)
Total liabilities			(10,483)
Equity (Deficit):
Retained earnings (deficit)			10,028
Treasury common stock			15
Total equity			9,306
Total liabilities and equity			(1,177)
Reorganization Adjustments [Member] | Predecessor [Member]
LIABILITIES AND EQUITY (DEFICIT)
Liabilities subject to compromise			11,570
Equity (Deficit):
Common stock			(27)
Additional paid-in capital			(4,818)
Reorganization Adjustments [Member] | Successor [Member]
Equity (Deficit):
Common stock			2
Additional paid-in capital			4,106
Fresh Start Adjustments [Member]
Current assets:
Contract acquisition costs			(91)
Income taxes and other current assets			(3)
Total current assets			(94)
Property, plant and equipment, net			(4,473)
Other intangibles, net			3,863
Other assets			(120)
Total assets			(824)
LIABILITIES AND EQUITY (DEFICIT)
Other current liabilities			(36)
Total current liabilities			(36)
Deferred income taxes			(168)
Pension and other postretirement benefits			(437)
Other liabilities			(28)
Principal outstanding			277
Total liabilities not subject to compromise			(392)
Total liabilities			(392)
Equity (Deficit):
Retained earnings (deficit)			(1,173)
Accumulated other comprehensive income (loss), net of tax			741
Total equity			(432)
Total liabilities and equity			$ (824)