Income Taxes - Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Provisional tax benefit, amount			$ 1,100
Purchase accounting adjustment		$ 92
Federal
Current	$ 7	(576)	82
Deferred	376	734	(988)
State
Current	15	(22)	21
Deferred	81	52	16
Foreign
Current	35	36	22
Deferred	(11)	(54)	(2)
Total income tax expense	503	170	(849)
Income tax expense allocation
Attributable to income	503	170	(849)
Stockholders' equity:
Compensation expense for tax purposes in excess of amounts recognized for financial reporting purposes	0	0	0
Tax effect of the change in accumulated other comprehensive loss	$ (62)	$ (2)	$ 81
Reconciliation of the statutory federal income tax rate to effective income tax rate
Statutory federal income tax rate	21.00%	21.00%	35.00%
State income taxes, net of federal income tax benefit	(1.60%)	(1.50%)	3.90%
Impairment of goodwill	(28.60%)	(36.60%)	0.00%
Change in liability for unrecognized tax position	(0.20%)	1.30%	1.00%
Tax reform	0.00%	(5.90%)	(209.80%)
Net foreign income taxes	(0.50%)	1.80%	(0.70%)
Foreign dividend paid to a domestic parent company	0.00%	0.00%	0.20%
Research and development credits	0.10%	0.90%	(1.40%)
Tax impact on sale of data centers and colocation business	0.00%	0.00%	5.00%
Tax benefit of net operating loss carryback	0.00%	9.10%	0.00%
Level 3 acquisition transaction costs	0.00%	0.00%	6.00%
Other, net	(0.80%)	(1.00%)	3.60%
Effective income tax rate	(10.60%)	(10.90%)	(157.20%)
Impairment losses	$ 1,400	$ 572
Operating loss carrybacks, amount		142
Tax expense related to sale of colocation business			$ 27
Transaction costs			32
Deferred tax assets
Post-retirement and pension benefit costs	1,169	1,111
Net operating loss carryforwards	3,167	3,445
Other employee benefits	134	162
Other	577	553
Gross deferred tax assets	5,047	5,271
Less valuation allowance	(1,319)	(1,331)
Net deferred tax assets	3,728	3,940
Deferred tax liabilities
Property, plant and equipment, primarily due to depreciation differences	(3,489)	(3,011)
Goodwill and other intangible assets	(3,019)	(3,303)
Other	0	(23)
Gross deferred tax liabilities	(6,508)	(6,337)
Net deferred tax liability	(2,780)	(2,397)
Deferred tax liabilities, noncurrent	2,900	2,500
Net deferred tax assets	118	131
Valuation allowance, DTA, increase (decrease), amount	(12)
Summary of reconciliation of the change in gross unrecognized tax benefits activity
Unrecognized tax benefits at beginning of year	1,587	40
Increase in tax positions of the current year netted against deferred tax assets	11	0
Increase in tax positions of prior periods netted against deferred tax assets	6	1,353
Decrease in tax positions of the current year netted against deferred tax assets	(49)	(15)
Decrease in tax positions of prior periods netted against deferred tax assets	(19)	0
Increase in tax positions taken in the current year	5	4
Increase in tax positions taken in the prior year	10	211
Decrease due to payments/settlements	(8)	(1)
Decrease from the lapse of statute of limitations	0	(2)
Decrease due to the reversal of tax positions taken in a prior year	(5)	(3)
Unrecognized tax benefits at end of year	1,538	1,587	$ 40
Unrecognized tax benefits that would impact effective tax rate	259	256
Interest on income taxes accrued	15	$ 17
Significant change in unrecorded benefit	3
Federal
Deferred tax liabilities
Operating loss carryforward	6,195
Summary of reconciliation of the change in gross unrecognized tax benefits activity
Unrecognized tax benefits at end of year	5,183
State
Deferred tax liabilities
Operating loss carryforward	18,000
Foreign
Deferred tax liabilities
Operating loss carryforward	$ 6,000