Fresh Start Accounting (Fresh Start - Balance Sheet) (Details) - USD ($) $ in Millions	Sep. 30, 2021	May 01, 2021	Apr. 30, 2021
LIABILITIES
Liabilities subject to compromise			$ 11,570
ASSETS
Cash and cash equivalents		$ (1,169)
Equity (Deficit):
Retained earnings (deficit)			10,028
Reorganization Adjustments [Member]
ASSETS
Cash and cash equivalents			(1,169)
Accounts receivable, net
Contract acquisition costs
Prepaid expenses
Income taxes and other current assets
Total current assets			(1,169)
Property, plant and equipment, net
Other intangibles, net
Other assets			(8)
Total assets			(1,177)
LIABILITIES
Long-term debt due within one year			(5,767)
Accounts payable			(6)
Advanced billings
Accrued other taxes
Accrued interest			(1)
Other current liabilities			53
Total current liabilities			(5,721)
Deferred income taxes			70
Pension and other postretirement benefits
Other liabilities
Long-term debt			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
Accumulated other comprehensive income (loss), net of tax
Treasury common stock			15
Total equity (deficit)			9,306
Total liabilities and equity (deficit)			(1,177)
Fresh Start Adjustments [Member]
ASSETS
Cash and cash equivalents
Accounts receivable, net
Contract acquisition costs			(91)
Prepaid expenses
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
Long-term debt due within one year
Accounts payable
Advanced billings
Accrued other taxes
Accrued interest
Pension and other postretirement benefits
Other current liabilities			(36)
Total current liabilities			(36)
Deferred income taxes			(168)
Pension and other postretirement benefits			(437)
Other liabilities			(28)
Long-term debt			277
Total liabilities not subject to compromise			(392)
Liabilities subject to compromise
Total liabilities			(392)
Equity (Deficit):
Retained earnings (deficit)			(1,173)
Accumulated other comprehensive income (loss), net of tax			741
Treasury common stock
Total equity (deficit)			(432)
Total liabilities and equity (deficit)			(824)
Successor [Member]
Equity (Deficit):
Common stock
Additional paid-in capital
ASSETS
Cash and cash equivalents			890
Accounts receivable, net			516
Contract acquisition costs
Prepaid expenses			92
Income taxes and other current assets			42
Total current assets			1,540
Property, plant and equipment, net of accumulated depreciation and depletion			8,547
Other intangibles, net			4,441
Other assets			398
Total assets			14,926
LIABILITIES
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		291
Pension and other postretirement benefits			1,726
Other liabilities			412
Long-term debt			7,015
Total liabilities not subject to compromise			10,818
Liabilities subject to compromise
Total liabilities			10,818
Equity (Deficit):
Common stock			2
Additional paid-in capital			4,106
Retained earnings (deficit)
Accumulated other comprehensive income (loss), net of tax
Treasury common stock
Total equity (deficit)	$ 4,108		4,108
Total liabilities and equity (deficit)			14,926
Successor [Member] | Reorganization Adjustments [Member]
Equity (Deficit):
Common stock			2
Additional paid-in capital			4,106
Successor [Member] | Fresh Start Adjustments [Member]
Equity (Deficit):
Common stock
Additional paid-in capital
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
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
Long-term debt
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 (deficit)			(4,766)
Total liabilities and equity (deficit)			16,927
LIABILITIES
Long-term debt			277
Equity (Deficit):
Common stock
Additional paid-in capital
Predecessor [Member] | Reorganization Adjustments [Member]
Equity (Deficit):
Common stock			(27)
Additional paid-in capital			(4,818)
Predecessor [Member] | Fresh Start Adjustments [Member]
Equity (Deficit):
Common stock
Additional paid-in capital