Income Taxes - Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Provisional tax benefit, amount		$ 1,100
Purchase accounting adjustment	$ (92)
Income tax expense
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Transition Tax For Accumulated Foreign Earnings, Provisional Income Tax Expense	11
Federal
Current	(576)	82	$ 335
Deferred	734	(988)	5
State
Current	(22)	21	27
Deferred	52	16	8
Foreign
Current	36	22	26
Deferred	(54)	(2)	(7)
Total income tax expense	170	(849)	394
Income tax expense allocation
Attributable to income	170	(849)	394
Stockholders' equity:
Compensation expense for tax purposes in excess of amounts recognized for financial reporting purposes	0	0	(2)
Tax effect of the change in accumulated other comprehensive loss	$ (2)	$ 81	$ (109)
Reconciliation of the statutory federal income tax rate to effective income tax rate
Statutory federal income tax rate	21.00%	35.00%	35.00%
State income taxes, net of federal income tax benefit	(1.50%)	3.90%	2.30%
Impairment of goodwill	(36.60%)	0.00%	0.00%
Change in liability for unrecognized tax position	1.30%	1.00%	0.20%
Tax reform	(5.90%)	(209.80%)	0.00%
Net foreign income taxes	1.80%	(0.70%)	0.10%
Foreign dividend paid to a domestic parent company	0.00%	0.20%	1.80%
Research and development credits	0.90%	(1.40%)	(0.60%)
Tax impact on sale of data centers and colocation business	0.00%	5.00%	0.00%
Tax benefit of net operating loss carryback	9.10%	(0.00%)	(0.00%)
Level 3 acquisition transaction costs	0.00%	6.00%	0.00%
Other, net	(1.00%)	3.60%	(0.20%)
Effective income tax rate	(10.90%)	(157.20%)	38.60%
Impairment losses	$ 572
Operating loss carrybacks, amount	142
Tax expense related to sale of colocation business		$ 27
Transaction costs		32
Foreign dividend paid to a domestic parent company			$ 18
Deferred tax assets
Post-retirement and pension benefit costs	1,111	1,321
Net operating loss carryforwards	3,445	3,951
Other employee benefits	162	112
Other	553	714
Gross deferred tax assets	5,271	6,098
Less valuation allowance	(1,331)	(1,341)
Net deferred tax assets	3,940	4,757
Deferred tax liabilities
Property, plant and equipment, primarily due to depreciation differences	(3,011)	(2,935)
Goodwill and other intangible assets	(3,303)	(3,785)
Other	(23)	(16)
Gross deferred tax liabilities	(6,337)	(6,736)
Net deferred tax liability	(2,397)	(1,979)
Deferred tax liabilities, noncurrent	2,500	2,400
Net deferred tax assets	131	434
Valuation allowance, DTA, increase (decrease), amount	10
Summary of reconciliation of the change in gross unrecognized tax benefits activity
Unrecognized tax benefits at beginning of year	40	16
Assumed in the acquisition of Level 3	0	18
Tax position of prior periods netted against deferred tax assets	1,338	2
Increase in tax positions taken in the current year	4	1
Increase in tax positions taken in the prior year	211	3
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	(1)	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	(2)	0
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(3)	0
Unrecognized tax benefits at end of year	1,587	40	$ 16
Unrecognized tax benefits that would impact effective tax rate	256	66
Interest on income taxes accrued	17	$ 56
Significant change in unrecorded benefit	12
Federal
Deferred tax liabilities
Operating loss carryforward	7,287
Tax credit carryforward, amount	52
Summary of reconciliation of the change in gross unrecognized tax benefits activity
Unrecognized tax benefits at end of year	5,526
State
Deferred tax liabilities
Operating loss carryforward	19,000
Foreign
Deferred tax liabilities
Operating loss carryforward	$ 6,000