Business Combinations (Details) - USD ($)			1 Months Ended				3 Months Ended								9 Months Ended	12 Months Ended
	Apr. 03, 2020	Nov. 26, 2018	Jan. 31, 2021	Dec. 31, 2020	May 31, 2020	Dec. 31, 2018	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Acquisition Cost Of Acquired Entities and Interest in Affiliates																$ 35,077,000,000	$ 9,000,000	$ 30,783,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt				$ 4,700,000,000		$ 7,784,000,000	$ 4,700,000,000									4,700,000,000		7,784,000,000
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable																33,166,000,000		7,960,000,000
Customer Contractual Obligation				$ 1,243,000,000			$ 1,243,000,000				$ 1,408,000,000					1,243,000,000	$ 1,408,000,000
Goodwill, Acquired During Period																$ 20,233,000,000
Rockwell Collins common stock par value		$ 0.01		$ 1			$ 1				$ 1					$ 1	$ 1
Proceeds from Issuance of Debt																		11,000,000,000.0
Proceeds from Debt, Net of Issuance Costs																		10,900,000,000
Net sales							$ 16,419,000,000	$ 14,747,000,000	$ 14,061,000,000	$ 11,360,000,000	$ 11,694,000,000	$ 11,373,000,000	$ 11,329,000,000	$ 10,953,000,000		$ 56,587,000,000	$ 45,349,000,000	34,701,000,000
Operating profit (loss)																(1,889,000,000)	4,914,000,000	2,877,000,000
Proceeds from Divestiture of Businesses and Interests in Affiliates																2,556,000,000	134,000,000	74,000,000
Total Assets				$ 162,153,000,000			162,153,000,000				139,615,000,000					162,153,000,000	139,615,000,000
Liabilities				88,269,000,000			88,269,000,000				95,289,000,000					88,269,000,000	95,289,000,000
Goodwill impairment									3,200,000,000							3,183,000,000	0	0
Amortization of Intangible Assets																2,125,000,000	1,244,000,000	736,000,000
Collins Aerospace Military Global Positioning System G P S And Space Based Precision Optics Businesses [Member]
Business Acquisition [Line Items]
Costs related to the divestitures required for regulatory approval								23,000,000								23,000,000
Proceeds from Divestiture of Businesses and Interests in Affiliates								2,300,000,000
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal								564,000,000
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal, After Tax								240,000,000
Income (Loss) from Individually Significant Component Disposed of or Held-for-sale, Excluding Discontinued Operations, Attributable to Parent, before Income Tax															$ 94,000,000		153,000,000
Collins Aerospace Military Global Positioning System G P S And Space Based Precision Optics Businesses [Member] | Other Income (Expense) [Member]
Business Acquisition [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal								595,000,000
Collins Aerospace Military Global Positioning System G P S And Space Based Precision Optics Businesses [Member] | Nonoperating Income (Expense)
Business Acquisition [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal								$ 8,000,000
Airborne tactical radios business [Member]
Business Acquisition [Line Items]
Proceeds from Divestiture of Businesses and Interests in Affiliates					$ 231,000,000
Gain on disposal recorded as an adjustment to fair value of net asset acquired					$ 199,000,000
Forcepoint [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Business Acquisition [Line Items]
Total Assets				1,900,000,000			1,900,000,000									1,900,000,000
Liabilities				855,000,000			855,000,000									855,000,000
Goodwill and intangible assets				1,400,000,000			1,400,000,000									1,400,000,000
Forcepoint [Member] | Forecast [Member]
Business Acquisition [Line Items]
Proceeds from Divestiture of Businesses and Interests in Affiliates			$ 1,100,000,000
Pratt and Whitney [Member]
Business Acquisition [Line Items]
Goodwill, Acquired During Period																0
Net sales																16,799,000,000	20,902,000,000	19,402,000,000
Operating profit (loss)																(564,000,000)	1,801,000,000	1,402,000,000
Total Assets				32,780,000,000			32,780,000,000				31,170,000,000					32,780,000,000	31,170,000,000
Goodwill impairment																0
Collins Aerospace Systems [Member]
Business Acquisition [Line Items]
Goodwill, Acquired During Period																(890,000,000)
Net sales																19,288,000,000	26,028,000,000	16,634,000,000
Operating profit (loss)																1,466,000,000	4,508,000,000	2,397,000,000
Total Assets				68,701,000,000			68,701,000,000				$ 74,049,000,000					68,701,000,000	74,049,000,000
Goodwill impairment									$ 3,200,000,000							3,183,000,000
Reporting Unit, Amount of Fair Value in Excess of Carrying Amount				$ 1,200,000,000			$ 1,200,000,000									$ 1,200,000,000
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount				7.00%			7.00%									7.00%
Impairment of Intangible Assets (Excluding Goodwill)																$ 57,000,000
Intangible assets, amount of fair value in excess of carrying amount				$ 110,000,000			$ 110,000,000									$ 110,000,000
Intangible assets, percentage of fair value in excess of carrying amount				7.00%			7.00%									7.00%
Total Segments [Member]
Business Acquisition [Line Items]
Goodwill, Acquired During Period																$ 20,233,000,000
Goodwill impairment																3,183,000,000
Eliminations and other [Member]
Business Acquisition [Line Items]
Goodwill, Acquired During Period																0
Goodwill impairment																0
Carrier [Member]
Business Acquisition [Line Items]
Shares of common stock distributed in the Distribution	866,158,910
Otis [Member]
Business Acquisition [Line Items]
Shares of common stock distributed in the Distribution	433,079,455
Rockwell Collins [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs																	$ 40,000,000	112,000,000
Payments to Acquire Businesses, Net of Cash Acquired		$ 14,900,000,000
Business Acquisition Cash Paid Per Share																		93.33
Business Acquisition UTC stock payable																		0.37525
Payments to Acquire Businesses, Gross		$ 15,500,000,000																$ 15,533,000,000
Shares of Common Stock issued for Raytheon Company outstanding common stock & equity awards		62,200,000
Noncash or Part Noncash Acquisition, Debt Assumed		$ 7,800,000,000
Noncash or Part Noncash Acquisition, Value of Assets Acquired		$ 30,600,000,000
Net sales						778,000,000
Operating profit (loss)						$ 11,000,000
Raytheon Company [Member]
Business Acquisition [Line Items]
Agreed Upon Number Shares of Common Stock of UTC which each share of Raytheon Common Stock will be Converted Into	2.3348
Fair value adjustments to fixed assets	$ 1,100,000,000
Fair value adjustment to future pension and postretirement benefit obligations	3,600,000,000			$ 980,000,000			$ 980,000,000									980,000,000
Customer Contractual Obligation	222,000,000
Goodwill, Acquired During Period	$ 21,500,000,000
Business Combination, Acquisition Related Costs																$ 142,000,000
Shares of Common Stock issued for Raytheon Company outstanding common stock & equity awards																652,638,000	0	0
Blue Canyon [Member]
Business Acquisition [Line Items]
Goodwill, Acquired During Period				266,000,000
Payments to Acquire Businesses, Net of Cash Acquired				426,000,000
Finite-lived Intangible Assets Acquired				$ 141,000,000