Restatement of Previously Issued Consolidated Financial Statements Restatement of Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net income (loss)			$ 193				$ 100	$ 409	$ 270	$ 652	$ 421	$ 860	$ 622	$ 366
Depreciation, amortization and accretion	$ 388	$ 393	394	$ 389	$ 385	$ 379	374	787	753	1,175	1,138	1,572	1,527	1,241
Increase (decrease) in other liabilities			(7)				(43)	77	76	179	179	254	271	234
Decrease (increase) in receivables			(43)				(5)	(89)	(59)	(166)	(74)	(96)	(105)	71
Net Cash Provided by (Used in) Operating Activities			512				452	1,227	1,110	1,890	1,773	2,698	2,500	2,032
Capital expenditures			(480)				(370)	(998)	(762)	(1,537)	(1,239)	(2,057)	(1,739)	(1,217)
Net Cash Provided by (Used in) Investing Activities			(489)				(384)	(1,010)	(777)	(1,549)	(1,279)	(2,081)	(1,793)	(10,482)
Net Cash Provided by (Used in) Continuing Operations			(5)				(95)	16	(103)	(88)	14	(75)	(26)	(258)
Cash, Cash Equivalents and Restricted Cash - Beginning of Period	429	408	413	453	336	345	440	413	440	413	440	413	440	697
Cash, Cash Equivalents and Restricted Cash - End of Period	325	429	408	413	453	336	345	429	336	325	453	338	413	440
Previously Reported [Member]
Net income (loss)			210				114	456	294	729	458		671	445
Depreciation, amortization and accretion	389			390						1,176			1,528	1,242
Increase (decrease) in other liabilities			(24)				(57)	30	53	102	144		223	175
Decrease (increase) in receivables														61
Net Cash Provided by (Used in) Operating Activities			512				452	1,227	1,111	1,891	1,775		2,502	2,043
Capital expenditures									(763)	(1,538)	(1,241)		(1,741)	(1,228)
Net Cash Provided by (Used in) Investing Activities									(778)	(1,550)	(1,281)		(1,795)	(10,493)
Net Cash Provided by (Used in) Continuing Operations			(5)				(95)	16	(103)	(88)	14		(26)	(258)
Cash, Cash Equivalents and Restricted Cash - Beginning of Period	429	408	413	453	336	345	440	413	440	413	440	413	440	697
Cash, Cash Equivalents and Restricted Cash - End of Period	325	429	408	413	453	336	345	429	336	325	453		413	440
Restatement Adjustment [Member]
Net income (loss)			(17)	(13)			(14)	(47)	(23)	(77)	(35)		(48)	(59)
Depreciation, amortization and accretion	0			0						0			0	0
Increase (decrease) in other liabilities			17				14	47	23	77	35		48	59
Decrease (increase) in receivables														0
Net Cash Provided by (Used in) Operating Activities			0				0	0	0	0	0		0	0
Capital expenditures									0	0	0		0	0
Net Cash Provided by (Used in) Investing Activities									0	0	0		0	0
Net Cash Provided by (Used in) Continuing Operations			0				0	0	0	0	0		0	0
Cash, Cash Equivalents and Restricted Cash - Beginning of Period	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Cash, Cash Equivalents and Restricted Cash - End of Period	0	0	0	0	0	0	0	0	0	0	0		0	0
Other Adjustments [Domain]
Net income (loss)			0	1			0	0	(1)	0	(2)		(1)	(20)
Depreciation, amortization and accretion	(1)			(1)						(1)			(1)	(1)
Increase (decrease) in other liabilities			0				0	0	0		0		0	0
Decrease (increase) in receivables														10
Net Cash Provided by (Used in) Operating Activities			0				0	0	(1)	(1)	(2)		(2)	(11)
Capital expenditures									1	1	2		2	11
Net Cash Provided by (Used in) Investing Activities									1	1	2		2	11
Net Cash Provided by (Used in) Continuing Operations			0				0	0	0		0		0	0
Cash, Cash Equivalents and Restricted Cash - Beginning of Period	$ 0	0	0	0	0	0	0	0	0	$ 0	0	$ 0	0	0
Cash, Cash Equivalents and Restricted Cash - End of Period		$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0		$ 0		$ 0	$ 0

Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3521-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3044-108585

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=98513485&loc=SL98516268-108586

+ Details

Name:	us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The aggregate net amount of depreciation, amortization, and accretion recognized during an accounting period. As a noncash item, the net amount is added back to net income when calculating cash provided by or used in operations using the indirect method.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

Name:	us-gaap_DepreciationAmortizationAndAccretionNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount after tax of income (loss) from continuing operations attributable to the parent.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4613673-111683

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.13)
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

+ Details

Name:	us-gaap_IncomeLossFromContinuingOperations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of increase (decrease) in operating liabilities classified as other.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

Name:	us-gaap_IncreaseDecreaseInOtherOperatingLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The increase (decrease) during the reporting period in the total amount due within one year (or one operating cycle) from all parties, associated with underlying transactions that are classified as operating activities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

Name:	us-gaap_IncreaseDecreaseInReceivables
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The increase (decrease) in cash associated with the entity's continuing operating, investing, and financing activities. While for technical reasons this element has no balance attribute, the default assumption is a debit balance consistent with its label.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3521-108585

+ Details

Name:	us-gaap_NetCashProvidedByUsedInContinuingOperations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3521-108585

+ Details

Name:	us-gaap_NetCashProvidedByUsedInInvestingActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3536-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3521-108585

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

Name:	us-gaap_NetCashProvidedByUsedInOperatingActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsToAcquireProductiveAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	srt_RestatementAxis=srt_ScenarioPreviouslyReportedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RestatementAxis=srt_RestatementAdjustmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RestatementAxis=cci_OtherAdjustmentsDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: