Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of components of provision for income tax

The components of the income tax expense are as follows:

	Years Ended December 31,
	2020		2019	2018
	(Dollars in millions)
Income tax expense:
Federal
Current	$	5	7	(576)
Deferred	338		376	734
State
Current	50		15	(22)
Deferred	55		81	52
Foreign
Current	29		35	36
Deferred	(27)		(11)	(54)
Total income tax expense	$	450	503	170

	Years Ended December 31,
	2020		2019	2018
	(Dollars in millions)
Income tax expense was allocated as follows:
Income tax expense in the consolidated statements of operations:
Attributable to income	$	450	503	170
Stockholders' equity:
Tax effect of the change in accumulated other comprehensive loss	$	17	(62)	(2)

Schedule of reconciliation of the statutory federal income tax rate to effective income tax rate

The following is a reconciliation from the statutory federal income tax rate to our effective income tax rate:

	Years Ended December 31,
	2020		2019		2018
	(Percentage of pre-tax income)
Statutory federal income tax rate	21.0	%	21.0	%	21.0	%
State income taxes, net of federal income tax benefit	(10.8)	%	(1.6)	%	(1.5)	%
Goodwill impairment	(71.0)	%	(28.6)	%	(36.6)	%
Change in liability for unrecognized tax position	(0.6)	%	(0.2)	%	1.3	%
Legislative changes to GILTI	1.8	%	—	%	—	%
Nondeductible executive stock compensation	(1.6)	%	(0.1)	%	—	%
Change in valuation allowance	2.6	%	—	%	—	%
Tax reform	—	%	—	%	(5.9)	%
Net foreign income taxes	(0.6)	%	(0.5)	%	1.8	%
Research and development credits	1.6	%	0.1	%	0.9	%
Tax benefit of net operating loss carryback	—	%	—	%	9.1	%
Other, net	0.1	%	(0.7)	%	(1.0)	%
Effective income tax rate	(57.5)	%	(10.6)	%	(10.9)	%

Schedule of components of deferred tax assets and deferred tax liabilities

The tax effects of temporary differences that gave rise to significant portions of the deferred tax assets and deferred tax liabilities were as follows:

	As of December 31,
	2020		2019
	(Dollars in millions)
Deferred tax assets
Post-retirement and pension benefit costs	$	1,164	1,169
Net operating loss carryforwards	3,138		3,167
Other employee benefits	119		134
Other	604		577
Gross deferred tax assets	5,025		5,047
Less valuation allowance	(1,538)		(1,319)
Net deferred tax assets	3,487		3,728
Deferred tax liabilities
Property, plant and equipment, primarily due to depreciation differences	(3,882)		(3,489)
Goodwill and other intangible assets	(2,755)		(3,019)
Gross deferred tax liabilities	(6,637)		(6,508)
Net deferred tax liability	$	(3,150)	(2,780)

Summary of NOLs

If unused, the NOLs will expire between 2023 and 2037. The U.S. federal net operating loss carryforwards expire as follows:

Expiring	Amount
December 31,	(Dollars in millions)
2024	$	745
2025	1,042
2026	1,525
2027	375
2028	637
2029	645
2030	668
2031	733
2032	348
2033	238
2037	2,976
NOLs per return	9,932
Uncertain tax positions	(4,855)
Financial NOLs	$	5,077

Summary of the reconciliation of the change in gross unrecognized tax benefits

A reconciliation of the change in our gross unrecognized tax benefits (excluding both interest and any related federal benefit) from January 1 to December 31 for 2020 and 2019 is as follows:

	2020		2019
	(Dollars in millions)
Unrecognized tax benefits at beginning of year	$	1,538	1,587
Increase in tax positions of the current year netted against deferred tax assets	18		11
Increase in tax positions of prior periods netted against deferred tax assets	5		6
Decrease in tax positions of the current year netted against deferred tax assets	(86)		(49)
Decrease in tax positions of prior periods netted against deferred tax assets	(5)		(19)
Increase in tax positions taken in the current year	4		5
Increase in tax positions taken in the prior year	1		10
Decrease due to payments/settlements	(1)		(8)
Decrease due to the reversal of tax positions taken in a prior year	—		(5)
Unrecognized tax benefits at end of year	$	1,474	1,538