Acquisitions, Dispositions, Goodwill and Intangible Assets (General Information) (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended		9 Months Ended
	Jan. 08, 2021	Apr. 03, 2020	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Business Acquisition [Line Items]
Goodwill					$ 53,789		$ 54,285
Proceeds from Divestiture of Businesses and Interests in Affiliates					1,074	$ 2,575
Assets					158,772		162,153
Liabilities					85,803		88,269
Forcepoint
Business Acquisition [Line Items]
Proceeds from Divestiture of Businesses and Interests in Affiliates	$ 1,100
Forcepoint | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Business Acquisition [Line Items]
Assets							1,900
Liabilities							855
Goodwill and intangible assets							$ 1,400
Airborne tactical radios business
Business Acquisition [Line Items]
Proceeds from Divestiture of Businesses and Interests in Affiliates						231
Gain on disposal recorded as an adjustment to fair value of net asset acquired						199
Collins Aerospace military Global Positioning System (GPS) and space-based precision optics businesses
Business Acquisition [Line Items]
Proceeds from Divestiture of Businesses and Interests in Affiliates				$ 2,300
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal				580
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal, After Tax				253
Costs related to the divestitures required for regulatory approval				20
Income (Loss) from Individually Significant Component Disposed of or Held-for-sale, Excluding Discontinued Operations, before Income Tax						94
Collins Aerospace military Global Positioning System (GPS) and space-based precision optics businesses | Other Operating Income (Expense) [Member]
Business Acquisition [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal				608
Collins Aerospace military Global Positioning System (GPS) and space-based precision optics businesses | Nonoperating Income (Expense)
Business Acquisition [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal				8
Raytheon Intelligence & Space global training and logistics business | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Business Acquisition [Line Items]
Assets					860
Liabilities					100
Goodwill and liabilities					660
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
Raytheon Company [Member]
Business Acquisition [Line Items]
Business Acquisition UTC stock payable shares		2.3348
Fair value of RTC common stock issued for Raytheon Company outstanding common stock and vested equity awards		$ 33,067
Fair value attributable to pre-merger service for replacement equity awards		99
Total estimated merger consideration		$ 33,166
Common Stock, Shares, Outstanding		277,300,000
Stock awards vested as a result of the Raytheon Merger		400,000
Total outstanding shares entitled to merger consideration		277,700,000
Shares of RTC common stock issued for Raytheon Company outstanding common stock and vested equity awards		648,400,000
Price per share of RTC common stock		$ 51.00
Goodwill, Purchase Accounting Adjustments			$ 61
Cash and cash equivalents		$ 3,208
Accounts receivable, net		1,997
Contract assets		6,023
Inventory, net		705
Other assets, current		940
Fixed assets, net		4,745
Operating lease right-of-use assets		950
Intangible assets, net:		19,130
Other assets		1,218
Total identifiable assets acquired		38,916
Accounts payable		1,477
Accrued employee compensation		1,492
Other accrued liabilities		1,921
Contract liabilities		3,002
Long-term debt, including current portion		4,700
Operating lease liabilities, non-current portion		738
Future pension and postretirement benefit obligation		11,607
Other long-term liabilities		2,368
Total liabilities acquired		27,305
Total identifiable net assets		11,611
Goodwill		21,589
Redeemable noncontrolling interest		(34)
Total consideration transferred		33,166
Fair value adjustments to fixed assets		1,100
Fair value adjustment to future pension and postretirement benefit obligations		3,600
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Loss Contracts		222
Business Combination, Acquisition Related Costs				26	$ 17	125
Net sales				14,747		47,668
Income (loss) from continuing operations attributable to common shareowners				$ 174		$ (2,328)
Basic earnings (loss) per share of common stock from continuing operations				$ 0.12		$ (1.54)
Diluted earnings (loss) per share of common stock from continuing operations				$ 0.11		$ (1.54)
Amortization of acquired Raytheon Company intangible assets, net (1)				$ 0		$ (270)
Amortization of fixed asset fair value adjustment (2)				0		(9)
Utilization of contractual customer obligation (3)				0		8
Deferred revenue fair value adjustment (4)				0		(4)
Adjustment to non-service pension (income) expense (5)				0		239
RTC/Raytheon fees for advisory, legal, accounting services (6)				23		119
Adjustment to interest expense related to the Raytheon Merger, net (7)				0		9
Elimination of deferred commission amortization (8)				0		5
Pro Forma Nonrecurring Adjustments, Net				$ 23		$ 97
Raytheon Company [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Finite-Lived Intangibles		$ 12,900
Finite-Lived Intangible Asset, Useful Life		25 years
Raytheon Company [Member] | Trademarks
Business Acquisition [Line Items]
Finite-Lived Intangibles		$ 5,430
Raytheon Company [Member] | Developed technology and other
Business Acquisition [Line Items]
Finite-Lived Intangibles		$ 800
Raytheon Company [Member] | Developed technology and other | Maximum [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life		7 years
Raytheon Company [Member] | Developed technology and other | Minimum [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life		5 years